If file associations are messed up on a specific user and the File Associations in Folder Options are correct, do this:
- Press [Win+R]
- Type regedit and press [Enter] to open Regedit (the registry editor)
- Navigate to HKEY_CURRENT_USER\Software\Classes
- Find you file type and see the software opens it. Usually the path to the software is messed up. Correct it and restart the computer.
I had a problem with .xls files on a single user like double clicking the file and nothing happened. If I opened Excel and did an Open for the file, it worked, but no double clicking.
NOTE: System wide file associations are in HKEY_LOCAL_MACHINE\Software\Classes.