Windows XP 64bit
ATI Radeon HD 4870
Acer x213W monitor
Sometimes, in some games mainly, my screen flashes white/black. If the game is windowed, then only the window flashes.
I doubt it's the monitor because I have two monitors and the same thing happens when I move the flashing window to the other monitor.
It doesn't ALWAYS flash but it flickers now and then and it gets annoying.