I had the same problem. I calmed down a bit to figure this out. In my case, I tried to open a new ASP.NET Core application and got 0 projects similar to the one described in this post.
What I tried: I tried to change environment variables in Control Panel \ System and Security \ System (click advanced settings)

Then click Environment Variables

Then check if the dotnet path is included, whether it is in the "Program Files" or "Program Files" (x86) section 
Some people have suggested moving up (x86) up based on Microsoft documentation
What solved my problem: it turned out that I had the wrong version installed and it was not compatible with Visual Studio 2017 
Then I deleted the other installations and reinstalled the version that is compatible with VS17 and works like magic. Hope this helps someone in the future.
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