Hit the f8 key at intitial boot and see if you can log into the safe mode. What did you do to your puter just prior to the problem statrting? If you can get into safe mode, do a system restore for a date just prior to the onset of the problem. You have some kind of hardware failure or driver conflict at startup.
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.