I have had this happen. If you have to break the needle an easy way is to also grasp it with a pliers, look away, and break it. If the screw that holds the needle in won't budge, then you will have no choice.
Sometimes, so much dirt and thread will bunch up to keep it from working. The other idea is to take the plate out, like kerly87 suggested, and untangle whatever is keeping it from running. Also, the timing belt might be off just a bit and something is not firing when it should be.
I wish you luck. PBP
Can you turn the wheel? It may be stuck in the bobbin. Can you open the throat plate and see the needle? If all else fails you may need to break the needle, I'd use a small wire cutter, and take the needle out. More than likely it is stuck either in the bobbin, or in a wad of thread. Good luck!
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