I'm trying to help my niece thread a machine that was given to her. I've followed the manual to thread the machine. Now I need to fill the bobbin. I've followed all the instructions & it won't fill the bobbin. Should the needle be going up & down, because it does & when I'm holding onto the thread around the screw behind the needle the thread in my hand just keeps getting longer & the bobbin never engages & fills. Very frustrating since I've been sewing for years. Please help.