This just happen recently and computer started locking up when on Norton 09 and trying to update antivirus when due.
The computer would just lock up and freeze a few weeks ago but with a restart I could get it going again. Now when trying to update Norton the screen will go to black and can't even wake it up.
The norton full scan and norton scrub/erase showed no problems. Possibly unrelated CLT/ALT/DELETE won't work either when computer freezes.
It seems to have happened after one of the updates several weeks ago.