Are you trying to clone a Windows 7 drive, but when you boot up it goes into a startup repair loop?  The startup repair doesn’t work though?

I recently hit this problem with a machine but the solution turned out to be fairly simple.

You have to boot into the recovery environment from a USB drive or CD/DVD.   Go into the command prompt and manually restore the registry using the files in the c:\windows\system32\config\regback folder.

Reboot and you should be up and running again!