Hello Joanna,
If you have made sure you have a perfect needle and it is in the correct way round then you may need to retime the machine, I can attach timing instructions if you email me but type in my address as you say it not as you read it because this site does not allow email addresses to be shown, make sure you give me your make of machine.
Ken
drivewithken at blueyonder dot co dot uk, November 2009
