Also check to see that your stitch length is not set on zero....I always increase my stitch length from 2.5 to 3 or more when quilting.
A friend recently called me to check out her husqvarna viking machine that was doing the same thing...we checked the usual things...threading and bobbin before noticing she had moved the knob to change the needle position and didn't have the machine set for any stitch. Sometimes it's the simplest of things that cause the problems.