Oh Windows, haha, sorry its been a while.
My guess is you installed Ionic and all your dependencies to one partition of the Harddrive, and you are trying to access them on another partition.
Make sure you install your dependencies (node/npm, ionic, grunt, etc) on the harddrive you'll be coding from.
Its kind of like opening an image. You have the image on one harddrive, so if you try to open it on a different harddrive, it won't exist. You know its a different harddrive becaues of the prefix C:/ and D:/