Go to http://www.dougknox.com and click on the Win XP Fixes (yes,, XP - it works on Windows 7 as well) link in the left hand column and then on File Association Fixes then finally the two fixes you need - EXE and LNK.
They are quite safe to download and run and they apply changes to your Registry to reassociate all the relevant files with the appropriate action. Restart your system and everything wlil be back to normal.
I downloaded the EXE & Lnk, however, my computer would not let me finish running!!!!! What do I do????