|This is the Vista forum so if it's a Vista machine insert your Vista disk and at the 'install' screen look for the 'repair' option bottom left - this should fix your boot problem automatically. If you haven't got a Vista disk you can download a Vista recovery disk from numerous places - HERE for example.|
If it's an XP machine - can you boot in safe mode? If so, then boot to the desktop, open 'My Computer', right click the 'C' drive, choose 'properties', then 'tools' and then 'error checking' The machine should reboot and run chkdsk. If you cannot get into safe mode then you need an XP disk to boot to the Recovery Console and then run chkdsk /r from there.
"I've always been mad, I know I've been mad, like the most of us..."