USB is very generic. If you aren't using a hub, the only other thing wrong could be the USB cable. I've seen them go bad when being connected and disconnected too many times. Try another cable. If that doesn't work. List your OS, processor, and the devices that you have connected to the computer. Whether they are on the USB connection or not. Probably the drivers are not working properly for one or more of those devices. Your first option would be to remove them physically, with the machine off. Remove them from the "Device Manager". Reboot clean, then re-install those devices.