Hello Jackie,
First of all take out the bobbin case, take out the race holder because there may be thread stuck there that is causing the machine not to move, if the machine does not move after doing that, you have a problem elsewhere, loosen off the stop motion as if to wind a bobbin and see if the balance wheel turn whilst pressing on the foot control, if it runs okay then the machine is truly jammed probably due to lack of oil.
Try the above frst, get back by e-mail if the machine is truyly jammed and I will guide you through it.
Ken
drivewithken@blueyonder.co.uk, September 2007