Your OS may need to re-associate certain extensions.
Download the .reg file here (the big green button that says (DOWNLOAD 632 B):
This should work for Windows 7 too. If not then try this registry edit which you create manually:
Please click Start-> Run. Type command and press Enter. Type notepad and press Enter.
Copy all the text below:
Windows Registry Editor Version 5.00
Save this as fix.reg to your Desktop (VERY IMPORTANT: Remember to select Save as file type: All files in Notepad.)
Double Click fix.reg and click YES for confirm.
Reboot the computer.
Let us know how that worked