How can I fix my Bernina 1120 sewing machine?

While sewing curtains all of a sudden the material would not move under the needle. I cleaned out all thread and fuzz, changed needle, changed bobbin, rethreaded the needle but no luck. I can sew and stitch is fine if I push the material along but that is not good when sewing large amounts of material.The machine is a Bernina 1120 that I have had no problems with for many years.