K7som+ wont boot os

i have an elitegroups, K7som+ motherboard, WD 80g Hd, 2 ultra 512 400mgh rams, a 256 ati radeon, and a pci networking card. I recently noticed the computer going slower and slower, so i was in the process of revamping the os. i wasnt doing anything critical, yet. I was doing basic hd cleaning. I rebooted the computer, and it wouldn't go through to windows, it would lag on the windows screen and pop up a blue screen. So i thought great i deleted something i needed. so i got a spare computers hd installed it and it did the same thing. So then i took the original hd and placed it in the spare computer, and it loaded fine. So then i removed all 3 cd drives and the floppy, i removed the networking card, and the video card(i switched to the internal video) i unplugged all accessories but the monitor and keyboard, and tried again to no avail. i also swapped the power supply and ram chips. all work on the other computers. i have also reset the bios. Any ideas?