What happens when you havnt got enough power out of your psu? because when i put my 430 or 5770 in the screen flickers and goes on and off, but is fine when i have an x700 in. Im guessing that because the x700 is older and has much lower performance it draws less power. I currently have an atx 550w psu
sometimes the pc just switches off and sometimes restarts, if that means anything, i thought that my cpu was on its way out. 