I recently got a new Windows computer and when I opened up an old Angular project I realized that I hadn't installed Angular CLI yet. So I installed it globally and tried it again. It still wouldn't work. When I typed "ng" on the command line it said it was not recognized as a command. I tried some other packages I know I had installed globally, like TypeScript. That didn't work either. WTF man!
Finally I discovered that there was a nodejs command prompt installed so I opened that and it worked from there. However that only fixed it for running from that particular command prompt. If I tried to run it in VS Code it still wasn't working.
So I opened up the batch file for the nodejs command prompt (C:\Program Files\nodejs\nodevars.bat) and noticed that it was adding npm to the path system variable. I looked at my path and I only had the nodejs path. So I added the path to npm, which I copied from nodevars.bat, and that fixed it.
Now that I think about it, this also solves a problem I had a few weeks ago when I created my own node app and installed it, but it wouldn't run from the command line. I figured I was just doing something wrong when configuring my app, but now I know I was right all along. Vindication!