rameven

My old PC- a Pentium 4 restarts itself when I shut it down. I have tried reinstalling Windows(XP then XP again then 7 then XP then 7 again and finally XP now!!!). What could be the problem? Its a P4 with 1GB x 2 DDR2 RAM(Even caused problem on a 512MB stick), some cheap PSU and I dont know...