I agree with Rodney -- this shouldn't be hard to fix yourself. I took apart the top tension on two of my machines. It's entirely possible that the tension release (when you lift the presser foot, the tension should let go on the top thread) is stuck. If you look online or on YouTube (I think ArchaicArcane on this board has posted some things either on her blog, or video, or both) you should be able to find the diagram of the various parts and where they go. When I take the tension apart, I just set each piece aside on a towel in the order that they came off, and in the position they need to be when they go on the tension assembly post. It's not too hard, trust me (if I can do it, anyone can).
Good luck!
Ila