This is the second time it's done it since I've had my PC, I've looked down and its randomly changed time. When I turned my PC on this morning it was fine, time was right 10:08, I played a little of the BFBC 2 single player game, close the game one hour later and now my clock says 3:36...
This happened like a week or so too.
Just an edit, it holds the minutes, date etc perfectly but the hour changes.
What is causing this?