First, pulll the battery off the Cmos with the power cord removed form the Power Supply. Keep it out for a couple of minutes and hit the power on button in the fornt of the puter with the psu still disconnected and then plug the battery back in. this will reset the bios to factory. If you are still getting the checksum error, which means the bios load is corrupted, you will need to flash the bios. Do the battery thing first and post the results.
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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.