My bad. No detail, correct. The screen freezes, the sound keeps playing, but no recovery. Even CTRL-ALT-DEL won't work. I have to hold the power button down to shut the PC off.
I experimented and shut off Norton 360's anti-virus auto-protect and 360 smart firewall, I played 4 hours and it worked fine, no freeze-ups. Maybe a Norton update is doing it? Any other suggestions?