Hi, you might be lucky and the registry backup's might work you will need a copy of the Vista OS dvd and boot from it, may have to access BIOS and set first boot device to cd rom.
• Boot from Vista DVD
• Get in to WINRE (repair your computer) option.
• Open command prompt
• Enter the following commands to fix the issue.
We need to determine what OS the RE assigned a drive letter to (not always C) so at the x sources prompt type:- bcdedit |find “osdevice” press enter (use the returned OS drive letter in the following cmds (assume C

.
NOTE:- Do not retype C:\windows\system32\ if that is the prompt just the rest of the cmd (config, config> ren default default old....etc)
C:
cd windows\system32\config
C:\windows\system32\config>ren default default.old
C:\windows\system32\config>ren sam sam.old
C:\windows\system32\config>ren security security.old
C:\windows\system32\config>ren software software.old
C:\windows\system32\config>ren system system.old
C:\windows\system32\config>cd regback
C:\windows\system32\config\regback>copy default c:\windows\system32\config
C:\windows\system32\config\regback>copy sam c:\windows\system32\config
C:\windows\system32\config\regback>copy security c:\windows\system32\config
C:\windows\system32\config\regback>copy software c:\windows\system32\config
C:\windows\system32\config\regback>copy system c:\windows\system32\config
Try to restart into normal mode, let us know how you get on.