If the correct driver for the USB Gateway/Microsft mouse isn't installed on your system, then that particular mouse will not be recognized by the operating system...
Shut down your computer...attach the USB mouse and see if the operating system recognizes it...if it doesn't and you still have the same issue...you will need to download and install a driver for that USB mouse. If you are having trouble finding the correct driver...give us as much info on the mouse as possible...model number, etc.
Other wise...try to find another mouse...you can find them cheap...try WalMart.