It's my kind advice to do a clean install of OS if possible,Contact Dell and request Dell Reinstallation Recovery CDs directly from Dell Technical Support. Contact them @ 1-800- 624-9896. Explain your situation. You will be asked for your service tag number of your system.
Hopefully Dell charges less than $15 to send you a replacement Reinstallation CD.
After recovery/Reinstallation don't pay any money for any antivirus programs!
Download & Install the following 3 freewares. It forms a free complete security suite for your system!
1. Avira Anvivir - http://www.free-av.com/en/download/index.html .
Avira is best & light solution for excellent overall system protection & internet security with real time updates, .