Extruder motor refuses to spin more than once

The only way I can get the motor to spin is if I hit the reset button on the RAMPS, then the next time I hit the Extrude button in pronterface it will spin but only that once. Any time after that it makes a buzzing sound but won't move, and I have to hit the reset button to get it to work again. I've tried adjusting the potentiometer but it doesn't help. The motor will work fine if I plug it into a different port, so I think it's something with the board or the software. I'm using sprinter. Any ideas on how to fix this?

UPDATE: the jumpers underneath the stepper driver were incorrectly installed. Fixed that and now it works.