I had a package that I wanted to install listed in the NuGet packages list but after clicking install, it seemed to wait a bit and then do nothing.

HOWEVER, clicking back onto the output tab in Visual Studio (since it was unhelpfully changing to the Error List tab), I noticed that there was a constraint that didn't allow the installation. In my case, the Microsoft.Net.Compilers package was too old for the NuGet package to install.

Once I saw that, it was easy to install the NuGet package after updating the other one!