I had this happen once and it was because the boot.ini file was corrupted. Do you have a Vista disk? If so put it in and boot the puter. You should be able to repair the boot file from there. Please come back and let us know how you did.

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EVGA 650i mobo with Intel e8400 Core 2 Duo
4 gigs OCZ 800 ddr2 ram and 160 gig sata hard drive
EVGA GTS 250 SC - Windows 7 - 64 bit
See my test at http://www.pcpitstop.com/betapit/sec.asp?conid=23014579