..installed all the latest drivers, specifically the BIOS update?
Hope this helps.
I recently put in a new videocard, motherboard and CPU up grading to an athlon 64 3000+. However I cant load windows with this new setup. I can full access my bios and such and everything seems fine until I get to the screen with the choices enter safemode, safe mode with command prompt, start windows normall etc, once a choice is made there the computer just restarts after a few seconds.