My Juki DDL555 Commercial sewing machine is jammed.?

Remove the presser foot and open the needle clamp. Cut the needle thread. Now try the handwheel. If it still won't budge, open the area around the bobbin case and start removing any lint, thread, and whatever you can see. Try again. If I still couldn't budge the handwheel, my next try would be to pull out the needle with a pair of pliers. Still no luck? I'd break the needle or cut it and keep wiggling and disassembling till I had it out.

If you're going to break or cut the needle -->> wear safety glasses, please! <<--

Inspect the sewing hook, bobbin, bobbin case, needle plate for damage from the needle. Buff out burrs and reassemble. Vacuum everything out, clean and oil per the manual. Try a test strip.

This one sounds hard enough that it may have knocked the machine out of time (see: http://tinyurl.com/smtiming) or maybe even clobbered one of the internal gears, so it may be shop time anyhow.

Juki Commercial Sewing Machine

As usual, Kay, your answer is excellent. I would, however like to say that I don't recommend breaking off the needle while it is jammed in the hook area due to the probability of damaging the machine. Another trick is to turn the hand wheel slightly backwards while pulling up on the needle as the hand wheel was going in the sewing direction when the needle jammed. If you cannot pull it out by hand, try this: Put a pencil about 2 inches away from the needle and lay a pair of pliers across the pencil and grip the needle firmly. Now press down on the pliers, using the pencil as a fulcrum. Try rocking the hand wheel as you do this.