So here's the problem. Sometimes, just sometimes (no definite time period) whilst playing L4D, the screen turns black and the sound loops. However, I don't require a reboot, all I do is alt+ctrl+del to bring up that nice choice menu, and then maximize L4D again. Again, L4D does not crash, it's still running. Tried turning off multi-core rendering and lower page pool memory ingame. Could it possibly be an application conflict?