How Do I Fix A Broken USB Port On A Mac?
First off, determine whether the USB port is faulty or if it's your USB device that's being plugged into the port. The best way to do this is to try multiple USB devices in the faulty USB port. Also try additional USB ports, if possible.
If it seems like the USB port is the problem, the most common solution involves simply resetting the Mac SMC.
Try resetting the SMC and hopefully that will fix your problem. If it doesn't, confirm that the port is faulty by testing other devices then run a software update (Apple menu > App Store in OS X). If it still doesn't work, your best bet is to make an appointment at a local Apple Store Genius Bar.