Had this problem on a Dell XPS M1330 running Vista and then upgrading to Win 7 64bit. Try flashing or updating BIOS first. Then unplug and replug (or replace if bad) the CMOS battery to reset BIOS. Remember CMOS holds the settings in BIOS. So when no power to CMOS, BIOS settings get wiped out (BIOS tells your pc what to do when it starts). Reset to default settings in BIOS. This fixed my restart issue! I tried all kinds of fixes and this was the only one that worked! Not all are software related issues. Any hardware changes can cause this problem like adding a IDE drive to a SATA board. Make the drive a slave changing it from cable select for example. Hope this is useful to someone.