Windows refuses to boot - registry issues

"Try logging in Safe Mode (boot & press F8) & make a new account (will mostly not work as HKLM is corrupted) or restore to a previous state using system restore.

If it fails, try repairing Windows again using the CD.

If it fails, I think you may need to clean install Windows again.

If you want to take a backup of your personal data present on the Windows drive (mostly C:) before you format, you can use many free tools which allow you to boot via CD (UBCD) or USB(Pen drive Linux)."

"Late to the party but this may help others.

Back up your Important data first, just in case you have a failing hard drive

http://www.howtogeek.com/howto/windows-vista/use-ubuntu-live-cd-to-backup-files-from-your-dead-windows-computer/

Perform a chkdsk, it may be the only thing that is wrong is file corruption, which this will attempt fix.

Boot from a Vista Install disk or use F8 and choose ""repair your computer"" if it is available.

Use the command prompt to run a chkdsk. Once you are at the cmd line, type the line below and hit enter key, it will take some time to complete, do not interrupt the process.

chkdsk /r C:

.

How to boot into the command prompt from a Vista DVD or F8

http://www.bleepingcomputer.com/tutorials/tutorial147.html"