Screen Flashes while moving mouse

Every so often, after the computer has sat unused for a short period of time a movement of the mouse will cause the screen to flash and programs to randomly open. I have tried replacing the mouse, reinstalling the mouse drivers, and reinstalling Service pack 4 to no avail. There is no screensaver currently installed. I also ran a virus check on the hard drive as well as checking the system settings in BIOS (making sure that power management was disabled). This problem doesn't seem to be associated with any software programs that are running. Does anybody have a clue?
The user describes the problem as occuring only after the computer has sat idle for a period of time. Its when the computer begins to "power" back up that the problem occurs.

I once had something like this and it turned out to be a stuck key! Try cleaning the keyboard or replacing it.