Problem could be bad motor, start capacitor, timer or speed select switch. This is a 3-speed motor. Try different speeds first if this model has a user controlled switch. With the pump removed and motor sitting on floor, with no power applied, can you freely spin the motor shaft? If so, put it in spin, when it's humming, try spinning the shaft by hand as fast as possible. If it starts, the capacitor is likely faulty. The best way to troubleshoot this problem is by taking readings with a multimeter but this is not recommended for inexperienced homeowners (probing live circuits) so your likely going to have to take the shotgun approach of replacing parts til its fixed. The motor is certainly a likely candidate as the contacts in the centrifugal switch can go bad but this is also true of the timer and speed switch.