Try this...
Have you tried resetting your parameters?
Restart and hold down the "option", "command", "p", and "r" buttons before the computer chimes. Keep holding till the computer chimes 3 times before letting go. This refreshes some of the system memory and will not harm your computer. Things like sound settings return to default...meaning it might kick in your USB to work again.
It this fails, use the hardware diagnostic in your install DVDs to check the hardware and/or the Mactools if you bought Applecare.
Let us know how if went/goes.