Video Problem (Screen Flash / Black)

Well first off I have windows 7 3 gigs of ram dual core amd processor and a 8900gtx+ i have 32 bit windows and ths is my problem.

This only happens when I (think) my video card is used more often.

Sometiems when i run 3 clients of this game i play called dekaron which is not hard to run i can run like 5 b4 it slows down. anyway every once in a while one of the clients will bug out causing my (entire) screen to flash and stuff dissapears then if i close the game (the bugging client) it stops. even tho i have it windows my background desktop bugs too anyway. one time i let it go on and do what it was doing and i love video signal to my monitor and then it came back and crashed the game itself. Im not sure wuts going on but it would be nice for some advice.

Are you over clocking any?
Check you graphic temps as the card may be over heating?
Check your P/S and make sure that you have a good steady power stream.