New PSU, still BSOD

Hello! The system I have at the moment is:
Abit KN9 motherboard.
Athlon 6000+ X2 CPU
Geforce 8800gts
6GB OCZ RAM
SATA Seagate HDD
SATA Sony DVD/CD

Recently the system froze breifly and then restarted XP 64 after about 3 minutes of launching and then would not reboot, variously the system would just restart after the logo screen or would go to bluescreen.

I first tried to boot the system using a knoppix DVD but it would hang at the udev hardware detection; I then tested the memory using memtest (no problems) and used seagate utils to test the disk.

After using a multi meter I detected a small amount of noise on the 12V rail of the PSU, so I replaced the PSU (old 650W, new 750W); when the PSU arrived the computer booted to windows XP 64 repeatedly and worked for an evening; this morning the computer seems to have returned to more or less the previous errors, although the computer this time will allow me to log onto windows I get Blue screen and restart after 2 mins (Before replacing the PSU it would not get as far as log in), and the same udev problem when trying to boot knoppix.

I would be grateful to hear any ideas as to what the problem might be...is it safe to assume that the motherboard is dead, or could it be the CPU...I ask because I am having a financial nightmare at the moment, so can't really afford to replace everything.

(I can't use the bluescreen viewer thing, because I can't use my machine for long enough!! Most bootable CD/DVD utils seem to work...is there a m'board diagnostic one out there?)