does the hand wheel turn freely by hand? does the needle move when turning by hand? Is the freewheel clutch knob tightened? (hold the balancewheel and turn knob clockwise.)
when the motor spins,
1) does its pulley also spin ? if not, loose set screw in pulley.
2) does the belt move but not the balance/handwheel, (loose belt)
3) if you give it a little spin by hand with the pedal depresse, does it turn but slowly. needs more cleaning and oil and perhapd brushes.
what did I miss? thread jams are common in these behind bobbin case. remove bobbin case and bottom cover and examine for threads. remove needle plate and examine for lint buikdup...