First open command promt (Start>all programs>accesories>command promt or Windows key+R and tpe CMD and hit enter)
Download CC Cleaner and remove Norton
CCleaner - Download
If that doesnt work.then type sfc/ scannow
This will try to repair windows files,i.e explorer.
If that says it found no problems,try a repair install to re-install missing or corrupted files of windows,this wont effect your data.