I had the same exact issue when installing MonoGame 3.7. I put up a thread on the forums and no one seemed to have experienced the same issue.
I sent a note to one of the MG developers but as of yet, I haven't heard from him.
I went back to version 3.6 where I had no issues. Except there is a MAJOR bug with the content-pipeline tool. With version 3.6, NEVER delete a folder in this tool as it will delete your entire project and somehow wipe it from existence so it is not recoverable.