Try resetting the PMU. A quick search with google should send you to apple's website with the directions. If that doesn't work....
Either your OS install has gone pooh city or the logic board isn't in good shape. Do the USB devices show up in system profiler? If they don't but your mice and such do, try booting off your Mac OS X install cd or dvd and check system profiler from there to see if your storage devices are detected that way. If they are detected when booting up off of the install media, its your OS. (possibly your user account? Try creating a new account and see if things work under the new account before reinstalling your OS.)