In Windows 8 & 10, you have to right-click devenv.exe
and select "Troubleshoot compatibility".
If, when you open Visual Studio it asks to save changes to devenv.sln, see this answer to disable it:
Disable Visual Studio devenv solution save dialog
If you change your mind and wish to undo the "Run As Administrator" Compatibility setting, see the answer here: How to Fix Unrecognized Guid format in Visual Studio 2015