Hi Mary,
As you have not used your machine for a while, have you checked the condition of the sponge bar?
Have you removed the carriage from the needlebed and tried to move the change knob? The old oil might be gumming up the works after so long - give the underside of the carriage a really good clean and re-apply machine oil to the moving parts. Do not use WD40 - knitting machines don't like it! Let the oil soak in and try the change knob again. Check that when you depress the cam buttons the various levers on the underside of the carriage move. Before you replace the carriage on to the needlebed wipe off any surplus oil with a clean cloth.
Hope this helps
Sue
January 2010