All of you with re-boot issues,
Check CPU temps, try new memory, turn off all power saving features in the OS and in BIOS.
CPU temp should be under 124F/50C for best performance. You may have stability issues (such as random re-boots) at about 160F/70C.
Disconnect the Cd rom,, or 2nd HDD if you have one,, (to determine underpower problem)
Ram could be the issue here,,,
cheers,
Try using one stick of memory in the first slot.