Just follow this step.
1. Boot up with the Vista Install Disc
2. You should see a screen that says "Windows is loading files"
3. After a few minutes you will get a language option. Select your language and hit next.
4. On the install screen select "Repair your computer"
5. Windows will find your copy of Vista on the machine
6. Select your copy of Vista and click next
7. You will now see the following options.
NOTed:-
* Startup repair - This automatically fixes problems that are preventing Windows from starting
* System Restore - This will Restore Windows to an earlier point in time
* Windows Complete PC Restore - This will completely restore your entire PC - programs, system settings and files - from a back up that you have previously created (Available in Windows Vista Business, Enterprise and Ultimate editions only)