II would guess overheating as a first principle too. Unplug it, take the back off and get the hoover in there. Also make sure that none of the case vents are obstructed.
If it all looks clean & good, fire it up and have a look in the error logs. Go to start>>computer, right click computer, select manage and open event viewer. In there, the pc will record errors ranked info, warning and critical. You may find out why by going through those logs.