do u have any more info like what u were doing when it stopped, what operating system ur using..... is that a desktop or laptop, do u have all the new updates from Microsoft installed? and what kind of devices you use in the usb port.... need more info then the model.
Shut down all power. Remove ALL USB connectors from your PC (and monitor). Reboot. Yes, you may now have no mouse or keyboard. If you still have them, shut down the system. If not, press the power button on your PC once (or maybe hold it for 5 seconds) to shut it down.
Reconnect USB devices one at a time, and reboot after each. You may find a defective device, or you may find that everything now works - the USB stuff was just locked up.