Well, from my brief experience with the 64 bit Win OS's, i found that getting compatible drivers was hard. Make sure you have the 64 bit version drivers.
I would first check the device manager and see if there are any drivers you forgot to install. You can also check the event viewer for clues to what happened with your system.
Right click on MyComputer > manage, then select the event viewer. Check the system and application logs for clues.
windows xp x64 restarts randomly 
Linear Mode
