I had a similar problem with my Bernina and the solution was that, even though I've been sewing for 50 years and on this machine for 3, I forgot to put down the pressure foot. I kept just repeating all the wrong steps - finally, I shut the machine off, rethreaded it, cleaned everything, went back to the usual thread I used before changing to the current one, and then realized that the step I was missing was putting down the pressure foot. When all else fails, though, take it to your dealer.