|It seems to me that you have too little power. Please list the specs of your power supply. Mainly: max amps on the +12 volt line, and the total watts.|
How many hard drives do you have? Have you recently added parts to your computer, and had this problem?
Do NOT continue to run games and/or processor intensive applications on this machine. It seems that the graphics cards are requiring too much power.
Find out if your computer will stay on without running anything processor intensive.