Hello Marion,
Check all of this first, make sure you have the bobbin in the bobbin case the correct way round, make sure you have the needle in the correct way round, make sure that when you thread the machine the presser foot is in the up position so the thread goes between the discs, the tension should be about 4 or 5, if you have checked all of that then the machine should sew just about perfect, if it does not then e-mail me, let me know what your model number is.
Ken
drivewithken@blueyonder.co.uk, August 2007