Elitebook 3850W screen wont turn on

Hi there, I was hoping someone would give me advice on how to fix my laptop before i take it to a laptop repair place. I have intermediate knowledge of computer systems myself, not greatly familiar with laptops though, I'm not too sure what is causing my problem but I've troubleshooted the best i can.

My Laptop: HP Elitebook 3840W HP EliteBook 8540W 15.6" Core i7 2.67Ghz 4GB GAMING LAPTOP 1GB GRAPHIC CARD | eBay exact listing i bought it from

My intention: I wanted to clean out the laptop and replace the thermal component as my laptop would often turn itself off due to overheating, that is it, the laptop would turn on and run fine.

What I've done: Replaced the stock thermal paste on the CPU and GPU with Arctic MX-4, removed the thermal paste with Arctic Clean Thermal Material Remover and used Artic Clean Thermal Surface Purifier (Arctic Silver ArctiClean Thermal Material Remover & Surface Purifier 60ml Kit: Amazon.co.uk: Computers & Accessories), got rid of all the dust, replaced my cpu cooler with a new one. Put it back together again.

What happens/My issue: My laptop powers on, my icon panel lights up, my laptop built in keyboard light works, cd drive works, the cpu fan turns on at full speed. My screen stays blank and does not turn on.

What i have tried to do to fix the issue:
- Took both sticks of ram out and turned the laptop on with both and just one stick of ram in, I have also tried replacing the ram with different sticks, nothing happens.
- Connect my laptop to an external monitor, does not recognize anything or turn on, I tried using the FN keys etc but nothing works.
- Took most thin strip wires out of the motherboard and try booting without them in, does not affect anything.
- Put the heatsink on without the GPU being in the socket and screwed in (just to test) laptop still turns on with the same issue
- Reapplied the thermal paste on the CPU and GPU a few times
- Used a brush to sweep any hairs or dust away
- Done the power trick issue which seems to fix most laptops (taking the battery out and holding the power button etc)
- Took the hard drive out and try booting, nothing happens
- Tilting my screen at an angle to see if the screen turns on
- Turned on the laptop with both the keyboard strip wires unplugged
- Turn the laptop on without the CPU fan in, just beeps if i remember correctly
- Turn the laptop on without any thermal paste on the CPU and GPU, same problem
- Unplugged both ends of the VGA port (inside of the laptop)

What i think it is: probably relating to the CPU? i'm really not sure, one of the pins is slightly bent on my inside VGA socket, if that is the cause i may have to order a new one of these Genuine HP EliteBook 8540w Dual USB VGA Port Board Cable LS-4952P 455N0P32L01 | eBay but the laptop still had the issue with the vga cable unplugged on both sides.
-none of the cpu pins are bent and look fine, slots and locks in perfectly.
- maybe something relating to thermal paste? i didnt put too much on, half the size of a pea

Anyone heard of this problem or can tell me some advice to fix it? Any help will be greatly appreciated.


Additional info:
My CPU: Intel Core i7 620M SLBTQ mobile laptop CPU 2.66 GHz Socket G1 4MB Cache CPU 0735858214025 | eBay (this one or looks very similar anyway) I put the thermal paste in the middle of the heat sink
My GPU: HP Elitebook 8540w NVIDIA Quadro Fx 880M 1GB Video Card 595821-001 | eBay I put the thermal paste in the middle of the heatsink too
- I made sure the thermal paste didnt go off the edges of the chips, should that not matter? or would i have to use more if it is a laptop? I'm mainly used to building PCs

- Conn0