Hello Christine,
First thing to do is to take out the bobbin case, drop down the gate and take out the hook or shuttle as some people call it and make sure there is no thread stuck in there, with those parts out see if the machine will run by pressing on the foot control slowly, some WD40 on all moving parts will help as well, any problems you can email me below.
Ken
drivewithken@blueyonder.co.uk, February 2009