Win 98SE Shutdown & Reboots

I had a problem with Win 98SE Shutdown & Rebooting I formated my hard drive instaled
win 95 than updated to win 98 than updated to
win 98SE I still have he problem with
win 98SE Shutdown & Rebooting by it self
the computer is a P233 MMX 128MB ram 10Gig HD
ATI XPERT Video Card, SoundBlaster 64 soundcard, CD-R and CD, DrectX 7.0 I think the problem has something to do with the VIDEO card or drivers can you help