I'm running a Windows computer with an NVidia graphics card with the latest drivers. When I run Heroes of Newerth (sweet computer game based on DotA if you care) and have other programs open, sometimes an error occurs. When it occurs, Heroes of Newerth continues to run without any problem whatsoever, but when I minimize it or close it the screen flashes black for about a second (one to three times) then stops. At that point whenever the video output should change (I move a mouse, open a program, change focus to another window) the black flash repeats until a static image should be displayed and it will stop flashing.

This has been happening for months during which my old monitor failed (unrelated) and the new monitor behaves the same way, leading me to conclude that the issue is not with the monitor. The new monitor offers either a clue or a red herring: When the flashes occur and the image is restored it displays the resolution which it only does when the resolution changes (switching to a full screen application, or different input; it is also a TV). These black flashes continue as described until the computer has been restarted. Manually ending and re-introducing explorer.exe does not fix the problem, nor does closing all "non-critical" programs. I'm stumped.

Heroes of Newerth is a fullscreen application. I suspect that running any instance of Adobe Flash Player (most notably for Bejeweled Blitz on Facebook games) produces the interference.

Windows XP Service Pack 2
AMD Athlon X2 4600+
ASUS M2N4-SLI motherboard
NVIDIA GeForce 7600 GT (Stop laughing. Stop that right now.)
4GB Corsair RAM

I am familiar with using the command prompt window, registry editor, and HiJackThis. I can produce a HiJackThis log if it will help, but it would be a wall of intimidating mumbo jumbo if it is unrelated.