Welcome to the boards Scarlett! pull the free arm off and check the feed dog drop switch back there. Mine is a little square button that you push either left or right, if you reach behind you can feel it, or turn the machine around to see it. You may have had it switched to feed dogs down position. It's easy to do accidentally if you took the free arm off for something. I've done it loads of times. Take the throat plate off, pop out the bobbin race, clean it well for any dust bunnies. My 4800 doesn't like anything to be caught down in there and a tiny piece of fuzz can cause havoc. Do those things, change your needle, totally re-thread everything and see if that helps. Also check to see if you have a build up of fuzz in the feed dog teeth. If so, an old toothbrush pops it right out. It will look like little pieces of felt.