How about the timing be off? What I mean is, does the hook blade of the bobbin housing line up with the shaft or the hole of the needle when you hand turn the needle knob to the front? You can see this by taking off the needle plate and opening up the bobbin area and removing the bobbin. Hand crank the needle down and watch where it lines up. If you have recently taken the housing out to clean everything, maybe the hook of the housing is not lined up with the needle coming down in order to catch the bobbin thread and draw it up. I may not be explaining this correctly. If you arent sure of how to do this, and you have a LQS or your service tech is close, I would think someone could assist you in getting it back in order. Just a thought anyway. I think you have been given almost every other answer. I sent you a pm that may or may not be the answer either.