Computer restarts itself on windows start?

Computer I'm trying to fix restarts itself when it gets past the windows login screen.

Tried booting to safe mode and same thing happens.

Tried restarting with the last good set up and again, same thing happens.

Tried using windows CD to do a repair install and again, same thing happens.

Tried putting the drive into another machine and same thing happens so it's definatly not the other components causing the issue.

Unsure what to do now as I can not get into windows to correct the problem at all.

Thanks for any help.

Computer restarts itself on windows start?house call

Seems the disk is OK... the MBR is able to locate the OS... so its a virus... or some other abnormal stuff...

Try running the PC via WIN boot CD... or a Win 98 bootable floppy disk...

Computer restarts itself on windows start?matchless

either your computers knackered or you have a virus, try formating your computer.
you will install fresh windows copy. if you unable to run windows installtion, check your HDD with third party software