What is a "knee press?" The only "knee-related" moving part I know in the sewing machine world is a knee lift (to lift the presser foot and have hands-free sewing).
I just ordered the Singer Quantum L-500 from HSN. The reviews are all over the place with this one so I asked on the QB. I figured if it's a dud, I'll send it back.
http://www.quiltingboard.com/t-43577-1.htm
Agree with the other comments though: Sounds like your machine needs to go back to emergency for additional surgery.