If you have a backup, restore, if not then

restore to factory settings in accordance with your user guide. That's in all likelyhood on your hard drive in the Start menu under All Programs -> Dell. If not, you can go to Dell's web site, put in your service tag, and download it.

When you've gotten your system back like you want it, I urge you to get yourself an external hard drive and a good 3rd party backup program. You can set it up to do everything automagically at the time and frequency of your choice. 1 TB external hard drives are about $70 these days and a really good FREE backup program is the Easeus todo backup free which you can download from
http://www.todo-backup.com/products/home/free-backup-software.htm . That can save you a lot of time and frustration the next time something like this happens. Sooner or later it happens to all computers for one reason or another.

Good luck.