Try refreshing your PC. In Windows 8(.1) you can restore your computer to factory, without affecting any of your files.
http://windows.microsoft.com/en-ca/windows-8/restore-refresh-reset-pc
Follow this link and follow the instructions for "Refresh your PC without affecting your files." You can also try "Restore your PC to an earlier point in time" if you have a restore point available that's not too far back.
Before you do anything, it's probably not a bad idea to back up all your files, or create a system image. Just in case.
Best of luck!