Apple - "USB device drawing too much power" error on startup with no devices connected
It could be a corrupt USB kernel extension. I'd try booting to Safe Mode:
- Turn off your Mac.
- Turn it back on and before you see the Apple logo on your screen, press and hold the Shift key until the Apple logo appears.
- A progress bar should appear below the Apple logo - during this time your Mac is performing a directory check and loads only necessary Apple kernel extensions (among other small things).
A feature of Safe Mode is that it reloads the kernel extensions from scratch, instead of from a cache file. It could be that during the Lion upgrade a kernel extension was damaged and has been cached afterwards.
Try the Safe Mode boot and see how it goes.
Good Luck!
In my case one of the metal prongs (cut out of the metal casing on the side without the connection pins) inside a usb port had been bent and was touching the other side, once this was corrected with a small screwdriver all my USB ports worked again and this error message disappeared.
This is probably the problem if you cannot fully insert a usb plug into any of the ports.
Another reason that this happens is when the device's USB cable is ripped/torn/ has a small hole. I had gone to sync my iPad with iTunes and suddenly was getting this message. The only other thing I had plugged into my computer was my printer, so I disconnected the printer. Then I tried again, but still got the message.
I was stumped so I started looking at the USB cable itself, and sure enough, there was a tear in it, and it was quite small but it was a tear in the cable that protects the wires inside. That was enough for it to cause the problem, but to be sure, I used my extra USB cable and was able to sync no problem.
After syncing with the "good" usb cable, I tried to sync with the bad one, and sure enough I got the error message again.
Sometimes you don't always see rips or tears in those cables. Maybe it got pinched behind something or whatever, but the smallest in it is enough to do it.
So that is another reason why some might get that " because a usb device was drawing too much power from your computer, one or more of your USB devices have been disabled" messages.