Since it's a motion issue, I'd stop tinkering until you do some research. The stopping and resetting suggests overcurrent, perhaps a motor stall, and the board resets and isn't trying to move anymore. It also might be a short to frame ground of one of the motor leads.
If you keep hammering it, you're likely to do more damage, it's time to find out what is wrong.
PS: the board is in the tender.
