I have an HQ Sixteen which I recently bought used. I have done a couple small quilts on it with no problem. I just loaded a new quilt on it, changed the thread both top and bottom. I have re-threaded it twice. But it is not picking up the bobbin thread when sewing, although it does pick it up when I do the needle down-needle up, but when I start to sew it does not catch the bottom thread. Help!!