It's not an unusual problem. I had to unwind thread for a long time from one of my machine handwheels. Usually there is a screw or pop out cover on the wheel itself to take off to see the guts of the wheel. When my Brother froze up the repair guy found a pin stuck in one of the machine gears. He said he has seen that before too. Usually it's something easy to fix with a new part or removing a foreign object.