"Because a USB device was drawing too much power from your computer, one or more of your USB devices have been disabled. To prevent damaging your computer, the USB device drawing too much power has been disabled. Other devices may have also been disabled. When you disconnect the device drawing too much power, your other USB devices will be enabled again."
I get this message on startup. I narrowed it down to 2 USB ports in the back. I had a asus wi-cast plugged in and it must have drawed too much power leaving the 2 ports disabled.
I see alot of laptops having this problem, but can't find much info for this problem on a mac pro.