iMAC - late 2011 USB Ports not working
USB Ports not working in iMac 2011. Hardware or driver issue(s).
iMac, OS X Mavericks (10.9.5)
If your lucky, then perhaps only the port overload protection was tripped by a bad cable or device.
To reset the port overload protection, disconnecting all of your USB devices and reset the SMC,
as per > Resetting the System Management Controller
1. Shut down the computer.
2. Unplug the computer's power cord.
3. Wait fifteen seconds. several minutes.
4. Attach the computer's power cord.
5. Wait five seconds, then press the power button to turn on the computer.
If that does not reset the USB ports, then you need to have the iMac serviced
If it does, then you may need to test each of your cables and devices individually, until you find the culprit.