It is possible that the USB ports are not turned on in the BIOS, in which case you will have to turn them on and see if that helps.
If you are using a USB mouse, disconnect the mouse, shut down operating system, turn system back on with mouse disconnected, when you see desktop appear, plug in mouse and this might then detect the mouse.
If no devices work, it is possible that the USB ports have burnt out as this can happen.
Another way is to turn the power off on your system, turn off from mains, turn back on after 10-15 seconds, turn back on system and this will find the USB ports.
Also, what operating system are you using as I have come across problems where you might have to upgrade the OS.
kenno1, May 2010