repair my desktop to factory

if not F8 . . usually F12 on newer Dells.

Dell usually delivers a recovery disc (DVD) with their systems, although at this late date, it may have gotten lost. You can often pick up a DVD from eBay to restore your system. Make sure it matches your version of Vista, and whether it is 32 bit or 64 bit. Also, you can restore with any Vista disc that matches your version by using the product key that is on the Certificate of Authenticity label.

Be aware that both of these options will destroy any data that is currently on your system, requiring a reload of any software you may have installed.