"USB device drawing too much power" error on startup with no devices connected
Solution 1:
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!
Solution 2:
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.