try using system restore on your user name. If you have a dell, then you should have recieved a CD for system restore. If you do not have a CD, try booting it from the computer (should be installed already if no CD) or go to Microsoft under a user name w/ administrative powers and ask for a system restore. You might be able to get a CD from your manufacturers also (dell, HP, alienware, etc.).
Alternately, (try this before system restore) try running your system in safe mode. If it works, hen make backups of your files, and then use system rstore.