Where is the pressor foot? The tension discs are usually closed when the foot is in the down position, this makes the thread hard to pull, When the pressure foot is raised, the tension discs release and it is easier to pull thread. Check and see if the tension discs are moving when you raise and lower the pressor foot. Sometimes thread or dust can get stuck in the tension discs and they need cleaning. Also make sure you have the machine threaded correctly and that none of the threading guides have thread wrapped around them. Is this a problem always, or is it just now that it is happening.