Thread bunched up in the shuttle race often causes the sewing machine to lock up.
Work the needle up and out of the shuttle race by rocking the hand wheel back and forth. You may be able to remove the needle from its clamp if you're not able to raise the needle out of the shuttle race using the hand wheel. Pull the fabric away and clear the bunched thread out of the shuttle race. Clean lint and debris out of the shuttle race; they can prevent the needle from hooking the thread, resulting in thread bunching up in the shuttle race and jamming the needle. Cleaning the shuttle race may prevent the sewing machine from locking up again once you resume sewing.
If thread bunches up again immediately after you start sewing and you thoroughly cleaned the shuttle race, then needle and shuttle hook synchronization may need to be adjusted. Adjusting the needle timing typically requires service by a technician, who has special tools to synchronize the shuttle hook with the needle.
