If you're able to open it up and get to the board, I'd start with that. Then post some pictures of the internals, you will want to look for broken solder points or split wires.
Thanks!
Was hoping someone could quickly take a look at these two videos:
1:
2:
Both are the same motor, essentially the motor will either start up and pulse, or it will just sit their and twitch.
I've tried re-connecting the "bullet" connectors (the wires to the motors) - which tricked me into...