|what you describe is a lockup|
This is related to hardware problems. Overheating is the first thing to check.
Put your hand behind the powersupply when running. Do you feel air moving from the fan? If not replace the power supply
Open the case. Blow out or vaccuum the dust bunnies. Make sure when on the fans are moving.
Check fan speed in the bios - just because they turn doesn't mean they are turning fast enough to move the correct amount of air.
Report back as to what you find.