If you have the Vista installation cd, boot from it. After you press the key, you should hear your DVD reader spinning up and then you will see a black screen with a white status bar at the bottom stating Windows is loading files.... After a while, the status bar will turn completely white and you will see a screen stating that Windows is loading. At the next few screens you should configure the Language to install, Time and currency format, and Keyboard or input method options so that they are set correctly. When done, press the Next button. You will now be at the main Windows Vista setup screen where you would normally install Vista on to a computer. Since you want to repair your installation, on the bottom left you will see an option that says Repair your computer. If no problems are found, go to advanced options, and click startup repair. That should fix it. Good Luck!