When you rock the wheel does it have a metal sound or just not move?
Is there dried up oil in the top part of the inside in the wrench like gizmo?
Have you oiled the needle bar shaft? You want to oil anything that remotely moves
then turn the machine in different directions so the oil will penetrate.
I had one machine with a bent needle bar shaft - nothing would move -
caused by someone pulling really heavy fabric through the machine.
Is the bobbin holder in the wrong position - check manual.
I had one someone had turned the bobbin shaft/bobbin holder just a hair - royal mess.
Is there some tiny little thread wrapped around/wedged in some moving part?
Are the pressure foot/thread cutter in the right positions?
Has someone tried to use the wrong size attachments and thrown the needle bar off timing?
Many things can cause a machine to freeze up. Have you been praying for patience???