I usually work on much older machines, but if the hook is not turning, it can be an indication of a broken gear. Otherwise, I'd turn the machine off, then on again to reset the computer. Completely rethread it, top and bottom, and try a new needle.

Thanks cooksnews. I'm afraid I've tried all of your suggestions to no avail. I just took it in for repair - I have a 6-year-old granddaughter clammoring for her Halloween costume so I have to get it fixed or I'll be in big trouble.

As a follow-up: the repairman told me that the problem with the bottom thread not being picked up by the needle thread was a timing issue. The thread jam caused the timing belt to 'jump' off track. He said he sees this frequently in the newer 'plastic' machines.

Just as a follow-up - I took my machine in for repair. It was a timing belt that had 'jumped' its groove. The repairman said that this is a common problem and can be caused by a minor fabric/thread jam. He said it is very common in the newer, lighter (plastic) machines.