Two of my dimm slots stopped working right

Hello,
I have an XFX 680 motherboard lga 775 running a duel core pentium 4 chipset E5700. 500 watt power supply. Had 5 gigs of RAM. EVGA 550ti graphics Card. After coming out of game KTOR it auto shut down on its own and would never or when it would it would freeze up booting back up. Now if I only use the first two DIMM slots it runs fine , but when I try to use the second set it freezes up or does not boot to BIOS at all. I know my RAM is good as I went and bought new ram and used them in the first two slots with no problems. What I am asking is there anyway a power supply could cause this as it sounds like it is straning to keep everything running. I flashed the bios and that did not help. Like I said the first two dimm slots run fine and computer runs ok, but when I try using the last two dimms it gives me a error message telling me to reset the fsb and memory timing. when I go into bios its where it should be?

I don,t know why it posted twice but some info I did not put in was Vista 64 bit. using corsair DDR2-800MHZ 2 GIG sticks

Thanks I will give that a try this evening!