Random reboots are often the result of a bad power supply and a weak PSU can cause the CPU fan to underspin and cause CPU temps to rise and the reulting mobo thermal protection shutoff in the BIOS to kick in. Plug in another pSU borrowed from another system and see if you have the same issues. If not, it's the power supply.
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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.