Here is the full list of all the "File association" steps that I've seen proved useful before. There is no need to go beyond the step that solves the problem but all the "your computer" & Microsoft checks are fine to do in any case - they would not do
any harm even if there was no fault.
On your computer
Control panel, Default programs, both Set your default programs and Associate a file type or protocol with a program
[IE check only] Internet explorer, Tools, Internet options, Programs - set Make default
Microsoft links [read the descriptions on the linked pages first]
Fix broken desktop shortcuts and common system maintenance tasks
Fixit When you run an .exe file on a Windows Vista-based or Windows 7-based computer, the file may start a different program
Diagnose and repair Windows File and Folder Problems automatically
Back to ones on your computer
Run both the Maintenance & Performance troubleshooters at Control panel, Troubleshooting.
Run the System File Checker *How to use the System File Checker tool to troubleshoot missing or corrupted system files on Windows Vista or on Windows 7*
There is additional guidance on it in *sfc.exe /scannow*
and then, if necessary,
3rd party links [read the descriptions on the linked page first to make sure it matches your symptoms - only go this far if you have to]
Default File Type Associations - Restore - Windows 7 Forums
http://www.slipstick.com/problems/link_restrict.htm
Cannot open Folders or Drives "This file does not have
a program associated..."
File Association Fixes for Windows 7
Best of luck.