Id say that if you start in safe mode and your computer crashes when scanning for virus's

(at what point does ytour computer restart, is it randomly? on start up or when you try to run programs. If it happens when you try to run programs, what programs trigger the crash (if any).

common sence says that ure programs are running on a system that cant handle them (as nihil pointed out) try a different O/S would be my suggestion.