I recently reformatted hard drive-reloaded WINXPhome and all appropriate drivers-system okay--Then I installed 3dmark5 and rivatuner I bumped up core to 500 from 300 --what I was using before format. That was 2days ago--now computer has rebooted itself 3 times today--always when I left click on something---the last time I was just deleting mail!! Also screen froze when I ran 3dmark5---which it did before format-(reason I did Format)But-I used to be able to run the benchmark to completion with no problem. The mobo is AsusP4s8x card GF6600gt Any advice will be appreciated!!