Hi Pat,
Have you checked the sponge bar? It may be that the foam has compressed and is not holding the needles firmly enough against the needlebed. Ideally the foam should be about 1/4 inch above the metal bar all the way along it. If it is not you need to replace it.
If the sponge bar is all right, you can check if there is a problem with the timing belt by setting the change knob to KC so that the carriage connects into the belt. You don't need to pull forward any needles but move the carriage to and fro to see if the belt rotates smoothly. Sometimes they do get damaged and if this is the case you will need to fit a new one. By removing the rear plastic covers you will be able to see the timing belt and the mechanism it is attached to. It may be that you just need to give it all a good clean and a bit of oil.
Hope this helps sort the problem,
Regards,
Sue, January 2011