First off, do you have a Dell? If so, many people have had this, and the solution is unknown. Dell Tech (the clueless-club) Support can’t help.
Have you tried System Restore? F8 gives you more options for SR via safe mode. If SFC doesn’t fix this, and you have a Vista CD you can try startup repair (fixes many things besides the inability to boot Vista):
Go to start >Run > and type in, appwiz.cpl. to get to add remove programs.
Try this link : http://support.microsoft.com/kb/925810/en-us
hope this will work 4 u.