Ask Max: Frozen 2008 iMac USB ports
Okay, last night I guess I loaded some shady applicationd onto my 2008 iMac. I restarted it, and when the computer loaded up again, the mouse was frozen in the corner but there was no LED light coming off from the keyboard or mouse. I connected my iPod with the USB cable and it wasn't charging. I then put in a disk (if I can ever get it out again) to see if the computer was working other than the USB ports, and yes, the computer works otherwise. So I'm assuming that my iMac USB ports are frozen, and I've restarted numerous times. No luck. Do you have any advice?
Since the USB system bus is hardware controlled, it's unlikely that a piece of software has rendered it inoperable. Try an alternative mouse first. Perhaps borrow one from a friend and see if it lights up.
Also try bypassing the keyboard and connecting directly to the iMac to make sure that the USB port on the keyboard hasn't failed.
If neither of those work, the next step is to reset the SMC. You will find instructions on how to do that in this PowerMax article.
Should none of these resolve the issue, I'd recommend having an Apple Hardware specialist take a look at the unit.