usb devices disabled

How can this be when I don't even have anything plugged into the USB cable
I do have a USB cable plugged into the back of my iMac

I can't get it to see my iPhone?

I rebooted and held the command button like I read earlier.

Anything else?

This forum post should help:

http://www.mac-forums.com/forums/apple-notebooks/310529-ever-popular-usb-devices-disabled.html