If you come across this problem type the word path in the command prompt and you should see something like this that says C:\windows\system32:
1. Right click computer and go to properties (or press windows key and pause/break).
2. Go to advanced system settings.
3. Go to environmental variables.
4. In the system variables browse to Path.
5. Edit it to say C:\windows\system32
6. Go to OK.
It should work now but you may need to restart your computer.