Go here and download the exe file association fix. It will download as a zip file. Unzip and double click the reg file. Do this in an admin account. If Double Clicking the reg file does not work try the below method.
NOTE: If your EXE file associations are corrupted, it can be difficult to open REGEDIT, or to even import REG files. To work around this, press CTRL-ALT-DEL and open Task Manager. Once there, click File, then hold down the CTRL key and click New Task (Run). This will open a Command Prompt window. Enter REGEDIT.EXE and press Enter. In the Menu bar select File Import and browse to the Reg file in the unzipped folder. Click Open.
If hamluis's suggestion does not work try the above fix.