Hello Leslie,
Check the simple things first, make sure you have presser foot up when you thread the machine, top tension usually about 4 or 5, make sure the bobbin is in the correct way round, if the bobbin thread is tight when you pull it just slacken off the screw on the bobbin case anti clockwise about a quarter of a turn at a time and test sew.
drivewithken, July 2010