If the gears are only "worn" they won't prevent the entire machine from turning. The timing and stitching will be affected and that can be seen on your sewing projects.
If the gears that drive the bobbin are broken everything else will turn, but the bobbin won't.
If the gears that drive the feed dog are broken then only the feed dogs stop.
Broken gears won't jam up the main shaft unless the debris gets between something and stops it.
dolores,
Perhaps you could set it out in the sun to thaw out .....
. That's a sorta kinda joke. If it is old oil then heat can soften it and the machine will turn. If it don't then I still vote for thread jamming things up.
Joe