PC won’t boot – Fault finding procedure


The author has been an electronics technician with many years experience in various fields. He tends to tackle electronic problems with a slightly different approach to most people.

He normally removes the motherboard from the case because, sometimes, apart from anything else, extra mountings have been added that can intermittently short out parts of the motherboard stopping it from working. It is also a good point to start by checking that the mountings have all been placed correctly and there are no extra unused mountings screwed into the back panel. Also visually inspect the board for any stray screws or other parts that might be loose or lodged behind it.

At the moment of opening the case, the very first check to be made is that there are no bulging or domed electrolytic capacitors to be seen anywhere. Any that are seen require immediate replacement! Once replaced continue with the instructions below.
(Check the cost for repair since it may be cheaper to buy a new board. Take into account the fact that you may require to replace the CPU and Memory should current boards not be compatible with your old Hardware.)

It is a good idea to place a sheet of wood on the work surface before dismantling the computer, both as an insulator and to protect the work surface. The wood should be thick enough to allow sufficient height (under the motherboard) for any cards that might be inserted later, so that the metal plate can drop over the edge of the wood. Without it, the card may well be pushed up and out of the socket causing serious damage to motherboard & the card.

The Power Supply Unit (PSU) is removed from the case for use, or alternatively use a known good spare. PSUs can usually be removed by undoing just 4 screws.

The following photograph shows work on an old P4 computer

It should be noted in the above photograph, that there is a grounding lead (RED WIRE) that is left connected at all times. When handling motherboards it is a good idea to earth yourself to discharge electrostatic build up that can cause damage to the delicate electronic components. Whilst the possibility of damage is reduced there is always the possibility of inflicting extra problems, so placing one hand on the power supply casing to discharge electrostatic build up is a wise precaution. Likewise keeping the power cord connected to the electrical supply ensures that, whilst Phase & Neutral have been disconnected, EARTH remains connected at all times, minimising possible electrostatic damage.

Initially, the motherboard, is set up in a minimum configuration with only the CPU, CPU FAN & minimum memory requirements. Sometimes motherboards require two memory cards in order to function. A graphics card may be needed if there is no built in monitor connector on the motherboard.

Ensure that there is means of access to the power on pins that are on the mother board. These require a momentary shorting to switch the computer on. They will also require several seconds of shorting to switch it off. To switch off, it’s better to use the power switch, if available, or pull out the plug.

The use of a multi-block power socket that acts as a switch is helpful to remove the power to all sockets being used. In the event that power needs to be disconnected quickly it gives a faster access and acts as an emergency power off button.

If the motherboard doesn’t have an on-board buzzer, make sure that a speaker is attached in order to hear any Power On Self Test (POST) warnings.

With this configuration it is easy to see if the motherboard will power up with the absolute minimum of components. It removes the possibility of having something in the case stopping the power-on process. It gives the ability to power up the motherboard and gain access to the BIOS (basic input/output system) settings. If there is no response to shorting the Power On pins then it is likely that the motherboard is faulty.

In BIOS it may be found that there are several configuration options for Power On in the event of an unexpected power failure.
The configuration frequently allows the choice of On, Off or Last.
This means that in the event of a power failure your PC will either Power On again, Remain Off or Return to the last condition before power was removed. It is frequently helpful whilst “benchtesting” (once you can gain access to the BIOS) to set it as last condition to save shorting out the power on pins. For boards that don’t have that option, a 1000μF capacitor with minimum 6.3V working voltage can be wired across an old reset switch & leads, then placed across the power on pins. When powered on it will act as a temporary short as it charges allowing “automatic” power on.

When you power up and beeping is heard with no visible monitor activity, power down and remove the memory. If the sound of the beep changes, it’s possible that the graphics card and/or the Monitor isn’t being “seen” by the CPU. The memory is checked before the Graphics card and Monitor so removal of the memory will help identify the location of the problem. If the beeping doesn’t change then it’s more likely that the problem is a memory access problem. That could mean Northbridge failure or memory failure.

The same applies when powering up, getting no reaction from the monitor and/or speaker. Power down and remove the memory.
Power up again and listen for any audible warnings (POST)

When the motherboard speaker is giving an audible warning, the motherboard is actually trying to start up (BOOT) but something is hindering output to the Display.

If, with no “on-board” memory installed, an audible warning is not heard, then the problem may be with the CPU or motherboard.

There is a possibility that there are problems with the memory. However, normally this would not stop the display from working. If possible try the memory in another computer to see if there is a similar response or even to run a memory test to prove it’s good. (There are instances where motherboards use on-board memory for on-board graphics cards. In this case, if the motherboard supports an additional PCI or AGP Graphics card, add one.)

Remove the Graphics Card and try another. If the graphics card is in an AGP slot, try using a simple PCI card in any PCI slot. Sometimes though, when the motherboard defaults to or has been set up to AGP first, the PCI will only work in a couple of slots, so try them all. Switching off each time before swapping the cards location.

Removal of the CMOS battery for a short while should restore the CMOS settings to factory defaults. Normally the factory default is for PCI. It doesn’t normally matter what PCI slot is used.

There are occasions when a faulty Motherboard refuses to allow the AGP to function but PCI graphics were OK. If a PCI card works then try another good known working AGP card or try the AGP in another PC if one is available.

One of the first things to do now, is check the motherboard to ensure that all jumpers are installed correctly and that nothing has been moved or is perhaps bridging the wrong pins.

One of the jumper blocks is for the BIOS. There are several possible configurations depending upon board manufacturer.
One position will force the CPU to use the NORMAL BIOS settings.
Another could force the CPU into BIOS configuration settings for maintenance, without requiring a combination of keyboard strokes at start up.
A frequently found setting is one that resets the BIOS to factory defaults, whilst another possibility, No jumper present, could force the Motherboard into BIOS RECOVERY mode that searches a Floppy drive for the BIOS firmware.
If the jumper is missing,or not making proper contact, the motherboard goes into AUTOMATIC mode and looks for BIOS firmware on Floppy in order to replace the installed firmware. In this state there is frequently NO DISPLAY on older boards!

Care should be taken not to take things for granted, since it has been known for these jumpers to develop a bad contact, even if, rarely, showing as fitted correctly but not actually physically making contact!
Be aware that sometimes the jumper links may be in position but can be faulty or not making proper contact. If you find one that is troublesome, replace it as soon as possible.
Sometimes, when fitting the jumpers in place, it is easy to miss the pin (running the plastic down the side of the pin instead of over the top) and it’s only seen afterwards by careful scrutiny of the pins.

After checking the jumpers have been installed correctly the next step is to test the CPU.

If possible, try a known working CPU. If another computer with the same type of processor is available, try the CPU in that machine. Also try the CPU from the other machine in the motherboard that has problems.
Make sure that you use a suitable heat sink compound like ‘Arctic Silver 5’. Without a heat sink compound between the CPU and the heat sink, there is a severe risk of burning out the CPU within a few seconds, especially with older AMD CPUs.

Once the CPU, memory and graphics card are proven to be functional, check the motherboard to see if it has emergency BIOS repair support.That is, see if there is a way to replace or upgrade your BIOS by use of a floppy disk. Check the website of the board’s manufacturer. Carefully read the instructions and follow them to the letter. Download the latest, or any, applicable BIOS for your motherboard and install it in accordance with the manufacturer’s instructions to a floppy disk. Add a floppy drive and set the motherboard to access the floppy drive to read and replace the BIOS. Never wait until you have your Board working and Windows OS installed to do the update. There have been too many instances of “bricked” motherboards caused during a BIOS update from within Windows.

Connect a floppy disk drive to the Motherboard & fit the power cable.

Using a floppy disk, as explained by the manufacturer, Power on and listen to see if there are any audible warnings from the floppy to be accessed. There is usually a click and whirring that occurs when the floppy starts to work.
Note: If you see the floppy disk light come on immediately you power on, power off and check the floppy disk cable. This event is usually caused by cable reversal. Make sure that both ends are connected /orientated correctly. The light should only come on when the floppy is actually being “accessed”. If the light was on and the floppy was inside at the time you may have to re-write the contents. The cable reversal frequently corrupts the contents.

Don’t power off unless you think that you have either waited too long and nothing appears to happen or after a long pause you haven’t heard the floppy drive to be accessed at all. The process usually takes only a few minutes.

If a new BIOS has been installed, start again from the beginning to see if the video output reaches the display. Start from minimal system to see what works and what doesn’t.

One other point that should be noted and checked from the start, is that the Video cable connector(s) should be checked to ensure that none of the pins has been bent when connecting to the socket(s). Don’t forget that there are two ends to a cable and not all cables disappear inside the monitors, especially on LCD type monitors. Check both ends.

If, after following all of the above procedures, the motherboard still refuses to boot, it would indicate that the motherboard is faulty and needs replacing.

Once this procedure has got you to the point that you can see a display on your screen, you can add a keyboard, access BIOS & change the configuration.

It’s now time to start adding components to see if everything works.

Additional components can be added one at a time to confirm all is well. Always switch off before adding or removing anything, including the keyboard.

Once the unit is working satisfactorily, the unit can be slowly re-assembled into the case. Do it slowly, not adding everything in one go.
If It fails again inside the case then look to see what is causing you problems. Only use the screw fittings & mountings where the holes on the motherboard are surrounded by a metal ‘ground’ that is about or slightly larger than the screw head. Any other fixing point may possibly be a cause of a short circuit and system failure again.

The author recommends SpeedSys. It is not possible to go directly to the SpeedSys site so go to this one . You will then see this:

Select the SpeedSys link indicated.

Speedsys boots from Floppy and also allows you to save results to the floppy in picture (.pcx) & text formats.

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  • Sabruquah

    My pc HP Pavilion p6210y cannot boot. It indicates “error cpu not supported and shuts down within seconds. Pls what is the cause and solution

    • Please post your query in the forum section of TSF.