Grunt on Windows 8: 'grunt' is not recognized

I've not had any issues with grunt on several different windows 8 machines.

If you open the folder: C:\Users\[username]\AppData\Roaming\npm

Do you have a file named grunt.cmd in this folder?

If not I'd maybe try npm install -g grunt-cli again, maybe from an elevated command prompt.

If this exists and you have C:\Users\[username]\AppData\Roaming\npm in your PATH environment variable then typing grunt from a command prompt should work.

Silly question, have you tried closing the command prompt and opening a new one?

Confirm your PATH is correct (and not messed up). Just type PATH from the command prompt. There's really no other explanation that makes sense given the error you're describing and the steps you've taken.

Normally, using the where grunt command would have found grunt.cmd in your path if npm is installed correctly and it has been properly added to the system path.