Hello Shelley,
Start from the beginning, when you thread the machine make sure the presser foot is up so the thread goes inbetween the tension discs fully, tension should be about 5, it will only vary slightly either way, make sure you have the bobbin in the correct way round with the bottom tension set so you should just about be able to pull the thread through with some resistence, make sure that the needle is in the correct way round if you have replaced it..
Ken
drivewithken@blueyonder.co.uk, October 2007