You are probably sewing merrily by now but if not-Be sure the bobbin is in the case correctly. Insert the needle with the flat to the left and thread the needle from the right. If the needle plate was taken off at some point be sure the base behind the bobbin case has the small finger like projection pointing upwards to fit into the notch under the needle plate. This mis-positioning had me stymied a bit the first time I cleaned up a FW. Have fun!