One of the unfortunate problems that we have in VS is that if you have a side by side install of 2 VS versions and uninstall one of them, we screw up your VS file extension associations.
I am working on a tool that will diagnose and repair the VS file associations.
I currently have the diagnose part working and when I find time (I hope soon) I will add the repair and reset code.
If you are interested I've shared the code here. krassimir