When my top thread is breaking I usually have the thread caught in the wrong place in the upper lever thing - I can't remember the name of it - sorry. Anyway, remember that "L" shaped thing that came with your machine? Use it to open the left side of the machine - be sure to turn off machine first. Then look for caught threads. IF you find any, pull them upwards - gently - very gently. My only other thought is to wonder if you've changed thread types recently and might not have bobbin thread balanced with top thread. Needle choice is always a factor, too.