Cannot use keyboard/Mouse in startup

[phnx90]

Recently, I had a BSOD after playing a game for about two minutes, after which the computer started displaying artifacts and restarted itself all the time.

My specs are:
Intel Core 2 Quad Q6600
Corsair DDR2-800 RAM 2GB x2
Western Digital 320GB HDD @7200 rpm
(Old GPU) XFX GeForce 8800GTS 320MB
(New GPU) XFX GeForce GTX 275 896MB
Asus P5B Motherboard
Corsair 620W PSU

I reinstalled Vista (was using Windows 7 at the time of the crash) SP0 but the artifacting became worse.

I figured it was the GPU, so I bought a new GPU (GTX 275) and the artifacts disappeared.

However, except for the first minute after I boot up the computer for the first time, I could no longer use the keyboard and mouse (stopped responding when a "Windows has detected a USB input device" or something like that). I restarted the computer. Again, the mouse and keyboard was responsive until the message came up.

I restarted it again, but this time the mouse and keyboard were unresponsive completely - I couldn't even use the keyboard to get into safe mode, or boot from disk.

Finally, I turned off the power supply and removed the CMOS for a few minutes and put it back, then started the computer. It said: "Overclock failed! Press F1 to get into setup or F2 to use existing (I think) settings" - keyboard still didn't work.

I have this feeling that when my computer first crashed, the motherboard AND the GPU may hav died...any ideas?

PS: Oh, and I didn't have the extra PCI express/6 pin cable for my GTX 275, so I used the adaptor that came with the card with a free 4 pin peripheral power cable, in case that is of any further help.

 

[Mongox]

You need to get a PS/2 connected keyboard to get into the BIOS, then set it to turn on USB legacy support for keyboard and mouse. I'd set the BIOS to optimal defaults to start with, then see if you can boot successfully, then change things to suit you.