Currently Being ModeratedNov 14, 2012 7:33 AM (in response to joegunner1)
Disconnect the drive(s) and restart your iMac and try again.
If that doesn't work and other USB or FireWire devices are also not working...?
Then reset your SMC, as per > Resetting the System Management Controller (SMC)
1. Shut down the computer.
2. Unplug the computer's power cord.
3. Wait fifteen seconds.
4. Attach the computer's power cord.
5. Wait five seconds, then press the power button to turn on the computer.iMac, Mac Mini, iPad, iPods, Mac OS X (10.6.8), (10.8.2), Safari, iTunes, iPhoto