hi mate, it could be this or not?? mine was doing the same, a few weeks ago (pc)symbols were dissappearing and then appearing all of a sudden..this went on for a while, tried all the stuff that you tried...installing, uninstalling, no luck..so i took the side off pc , then removed the ribbon cable that connects the dvd drive to pc..found that it was rubbing against the fan, and it was this, that was causing it to act funny ,replaced the cable no problems since... you have to look very carefully at the cable it was very minute rubbing...mark.