Hi my GA-EX58-UD5 last firmware 12 gb (2gb sims) 920 cpu been having problems on and off for a month now

,before i changed my psu it was turning its self off or would not turn on at first it would go on and off

antec 850 watt was 4 years old, got a new antec 850 watt but its been locking after working fine for a few mins up, so only the screen is displayed and have to reset the machine, dont get the blue screen but i`m getting FF on the post LCD which comes up as a graphic card fault but can play games fine and any thing else and most times it does not lock up at all !!! i`ve cleaned the contacts on the ati 5870 with no change

tryed it in the other slott as well and still the same .. graphic card or PSU
