Cant boot, keep getting repair option

Hi,

Trying to fix a Dell desktop running Vista Basic. Just keeps going to repair PC option but never fixes problem (Seems to say corrupt registry). I tried system restore option and although it shows lots of restore points it always fails.

Wont start in any safe mode options.

I did an image copy to another hard drive and did a factory restore which worked ok so the files appear to be there.

I know with XP I can go into command prompt and manually replace the system, software, sam etc. files but don't know if it can be done in Vista or if anyone can suggest anything else.

Thanks for any help