By any chance did you try to unjam the printer while it was still powered on? You should always, ALWAYS clear head jams with the machine off and unplugged to avoid damage.
The head lock bracket is located on the top of the carriage rail. If you remove the top cover over the maintenance area, you can see it. Release it, slide the carriage out a few inches, and try to power on again. If you get the same error, chances are that the motor driving chip has been blown.