(I put this in the motherboard section because it concerns a number of parts and I wasn't sure what the most major one would be)
I am absolutely stumped by this. I'm not going to list what I have tried because a list of what I have not tried would be more appropriate, and I don't know what I haven't tried!
I had a system as follows:
Dell Dimension 9100 aka XPS 400(Intel 945P Express chipset on MoBo)
Intel Pentium D 960(3.6 Ghz, 4MB L2 cache, dual core)
DVDRW drive paired with CDRW drive in IDE as master/slave
Dell Card Reader(Internal USB 2)
SB live! 24-bit 5.1 sound card(PCI)
2-port USB 3 card(PCIe x1)
5-port USB 2 card(PCI)
XFX AMD Radeon HD 6670 1GB GDDR5(PCI-e x16)
TP-LINK 300MBps Wireless-N card(PCI)
Green 500 Watt PSU(EXTREMELY BUDGET PSU- GREEN IS ACTUALLY THE BRAND)
A 120mm case fan and a 140mm CPU fan and a 3-pipe heatsink
Intel 320 series 80GB SSD(SATA II)
Seagate Barracuda 7200 RPM 160GB HDD(SATA II)
Windows 7 Ultimate 64-bit Service Pack 1
this system always worked fine for me in every way, except for one thing;
the HD 6670 always ran at PCIe x1, instead of x16, detracting from its performance. This never bothered me too much, as it worked okay as it was, but I was confused as to why it did that. After I was unable to fix it or gain an idea of why it did that, I just let it be and ignored it. Also, there are 3 ever-so-slightly bulgier than normal capacitors in the corner of my 9100/400 board. I know from experience how troubling worn-out caps can be, but these are not bulgy enough to seem remotely problematic and I have never had any trouble from them.
Recently, I decided to upgrade to a better PC. I bought the following in good condition and either new or used and certified working:
Intel Core 2 Quad Extreme QX9650(3 Ghz, 12MB L2 Cache, Quad Core)
Dell XPS 430 Motherboard(with Intel x48 chipset on)
Dell XPS 430 Case (with front panel/power button and HDD activity indicator light and fans very similar to those in the 9100/400)
DVD RW Drive (SATA II)
Dell XPS 430/420 Card Reader(internal USB 2)
4 sticks of 2 GB each DDR3-1333 RAM (8GB total)
XFX Pro 550 Watt Full Wired PSU(definitely NOT a cheapo PSU)
and I took the following from my old rig to put in it:
the USB 3 card
the USB 2 card
the wireless card
and the Radeon HD 6670.
If it had worked, then you wouldn't be reading this.
I did numerous tests and- I'm sorry, did I say numerous? I meant ABOUT ONE HUNDRED AND SIXTY tests, and I discovered that no matter what I put where and what extra hardware that I have in my extensive collection of parts I used and what other PCs I tested things in, everything works great in every combination I can possibly imagine except for one: If I put the HD 6670 in the XPS 430 MoBo.
What happens is this: After I plug the 6670 in and power the board, it turns on by itself, with the fans on, and the CPU fan on the ridiculously loud highest setting(if I have the fans plugged in)and has the MoBo) and power button lights (2 blue) on and turns on the HDD activity light on for a fraction of a second(if I have any H1Ds or the lights plugged in). It does not do anything else. One second later, it turns itself off and back on twice. It then does not give any feedback, make any noise from the speaker, or display anything on the screen, caps lock num lock and scroll lock do not do anything on a keyboard if plugged in(nor does any other keyboard input). It just sits there with the lights on and the CPU fan on high. There is a fan on the HD 6670; that comes on, but only the CPU fan goes on high. The heatsink on CPU is definitely good enough; the original XPS 430 would use the same one. It must be turned off by cutting power or connecting the two wires the power button connects for a few seconds. It can then be turned back on by pressing the power button, with the same results except that it does not turn itself off and back on twice. It only does that when it is first supplied power. It only gets to this if it has ram and a CPU in it and both the 4pin cpu and 24pin board connectors are in. Otherwise it gives normal errors for no ram and/or no CPU. I even tried it with the Pentium Ds I have, which use the same lga775 socket and have a FSB speed compatiable with the x48 chipset (800Mhz), though I did not expect them to work because they are not supposed to work on that chipset or BIOS. (speaking of BIOS, there is only one version of the BIOS from dell for that M/B, so no BIOS update) It acted like they were not there. As a warning: DO NOT EVER PUT A CPU IN A BOARD UNLESS THE FRONT SIDE BUS SPEED OF THE CPU IS SUPPORTED BY THE CHIPSET, ESPECIALLY IF THE FSB OF THE CPU EXCEEDS THAT SUPPORTED BY THE CHIPSET!!! I am glad that I didn't have to learn the hard way on that one.
Anyway, I can't possibly figure out i the remotest what could be the problem. As I said before, I have tried every combination and tested everything I can in other PCs(and that one itself without the HD 6670, but a different GPU, in) and it's just that board with that GPU. I just don't understand why they don't get along!
If you have any ideas, please tell me! If you want pics, tell me and I'll post!
I think that it might be possible that, through some crazy Dell OEM madness, the board won't power more than a certain amount through a PCIe slot, no matter what the limit of the PSU is? Because the original Dell XPS 430 graphics card took a PSU connector, and so did not get all of its power through the PCIe slot. My Radeon HD 6670 gets all of its power through the PCIe slot. Do graphics cards that have a PSU connector get all the power that a PCIe slot is SUPPOSED to deliver, and then some with the PSU connector, or do they get the bulk of their power through the PSU connector and just use the PCIe slot mainly for communication with the board?
EDIT: The USB 3.0 card takes an optional floppy-drive-style power supply connector. Not that it matters.