I always start by assuming that I have a virus. Get ccleaner from www.ccleaner.com. Run that. Then, over on the left hand side click on registry and run that program. If you are still having trouble download antivirus Avira from http://www.free-av.com/en/download/1/avira_antivir_personal__free_antivirus.html
Make sure you get the free version and run it.