Vista wont boot after virus removal

Pardon the interruption..I have a Vista Business laptop (inspiron 1720) that refused to boot past the initial Vista boot screen (you know, the one with the progress bar on it, and nothing else)I ran a virus scan from a boot cd and found three viruses, which the AV removed. Still, no joy. I removed the hard drive, plugged it into an external enclosure, plugged it into my desktop and re-ran an AV scanner. This time, it found 5 viruses, which were all successfully removed. After reinstalling the drive in the laptop, it still won't get past the progress bar screen. Any ideas? I have tried booting into Safe Mode, no joy, "Repairing My System", no joy. I even updated the BIOS using an iso boot cd and the latest BIOS image from Dell. I'm at a loss. Any help is appreciated.