I would run memtest86 on that memory. Have you checked to make sure that the CPU fan is functioning? Your CPU could be overheating. The PSU is easy to test if you can swap out a PSU from another puter, wether yours or a friends, and temporaily run you puter that way. You simply need to plug in the test PSU externall(outside the case). Pull the mobo power connector(s) carefully and all the hd and cdrom etc aux power connectors and repower them from the trial PSU. If all is good then your PSU is bad, otherwise it's memory or overheating cpu.
Noli Nothis Permittere Te Terere!!
EVGA 680i, Dual EVGA 8800GT'S (650/950), 4 gigs OCZ DDR2 1066, Intel Q9450 at 3.8 Ghz, Koolance Water Cooled, Dual Plextor16x DL DVD+/-RW. Dual WD 250gb 16mb Cache Sata 3.0. 3DMark06 score = 19,168.