When installing the MonoGame Framework for Windows you may encounter an error where in the MonoGame installer all the boxes for the templates for each Visual Studio version are grayed out.
To fix this you need to make this directory:
"C:\Users\[USERNAME]\Documents\Visual Studio 2013\Templates\ProjectTemplates\Visual C#\MonoGame",
Where [USERNAME] is your user folder,
Then head to the registry editor (Win+R>regedit.exe) and goto this location:
"HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\12.0", click the "12.0" key,
Right click the open white space then click 'New>String Value' and name it "UserProjectTemplatesLocation", double click the string value you just created and give it the value of the project templates location which is: "C:\Users\Tom\Documents\Visual Studio 2013\Templates\ProjectTemplates"
Re-Run the MonoGame installer and you should have a checked box instead of a grayed out box.
The problem I encountered was a little different, but thanks for pointing me in the right direction.
In my case, the issue was that I was installing MonoGame under an account that is not an Administrator account. The installer tried to look for the registry value under the Administrator account's HKCU instead of the current account.
Changing my account type from Standard to Administrator and then installing it using my own account instead made it install the templates successfully.
(Changing it back to a standard account afterwards didn't cause any problems.)