The problem could be with your PSU, and your computer simply isn't getting enough power, or far more likely is that you have a corrupted version of windows installed. Try formatting the drive and reinstalling windows from scratch. If you are relunctant to do that, then try running the windows repair utility and searching for corrupted files. This might work, but there is no garrentee.
edit. oh, and check to make sure that you have the 4/8 pin PSU connected to your motherboard. I know that this can frequently cause your PC to restart at boot-time.