Hey everyone, Mike here.
So we had some issues with ionic not being able to be installed or throwing some errors with windows yesterday.
We push a few fixes and are hoping that everything is squared away.
Please install the latest version of ionic cli and test it out.
$ sudo npm install -g ionic
To verify that you have the latest version
$ ionic --version
This should give you version 1.1.4
If you are still having issues, please submit an issue so we can find out whats going on.