In some cases the motor shaft can bind, pull and push gently axially (up/down if normally mounted) and see if it losens up.
Normally the motor should turn fairly easily if rotated by the pulley by hand but put a voltmeter to the motor leads with the Beocord in play mode. Should read something like 12-14 Volts (DC).
No voltage (or very low) = fault in the power supply. If the old belts were a complete mess, they may have blocked the motor. There's a resistor in the power supply...
Voltage OK but motor doesn't rotate = replace motor (new ones in stock here).
Martin