if you boot from CD/Dvd as in a new install eg.boot set in bios to boot from this rather than Hdd as first option.
You will find option to Repair Windows Vista.or maybe new install or whatever?
You run the repair option,it will scan an fix many corrupt files,an vista will boot an run.
But then in the first place How do you know Windows is corrupt?Well?Tell us,What you know Clearly? an we can help.