I own a Nordictrack A2350 treadmill. The past month while running the speed has seemed to speed up and slow down at random times. Almost like the belt was slipping for a second. The other day while running the motor just stopped. All other functions work to include the incline, but now the treadmill belt and motor will not turn. The main belt to the motor is in good condition. The running belt will turn if I move it by hand. Any idea on what part I need to replace? Would it be the motor or some other part that it broken and is there a way to determine what part needs replacing? Thanks in advance.