Best answer as chosen by user stickman5758: Restore to factory settings
If you don't have a full system backup (which everybody should but many don't), I'd copy any data I wanted to keep and then restore to factory settings. You should've burned the discs needed to do that when you computer was new, but if you didn't, you can contact your manufacturer to see if they will send them to you for a small fee.
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.