I too bought a used Nolting and absolutely love it. They brought it to my house one evening around 8 pm on the way to the Denver Quilt show, set it up and stayed until nearly midnight working with me. After about 5 weeks and 16 hours of quilting, the motor went out on it. We niagnosedthe problem over the phone, again after hours, They sent me a box, paid my shipping both ways, and replaced the motor under the 1 year warranty I was given with the machine. I have to say they have excellent customer service and I am very happy with them. My closest dealer would be almost 3 hours away.
BizyStitches, you need to call the manufacturer. I am thinking you probably need a new tension spring or a new assembly which are very easy to replace. I had that happen on my 1st machine. It didn't matter what I did, the thread was breaking and the tension spring started sticking in the bottom position and I couldn't turn the knob at all. We took it apart and cleaned the assembly, put in a new spring and it worked like a charm.