After all the re threading make sure your needle is all the way up into the holder and put in facing the correct way. Ask me how I know this. My needle did this when not quite all the way up into the holder!

Rethread your machine. If the issue is under the fabric it's the top tension and if its on top of the fabric its the bobbin tension. This happened to me this weekend and I'd been sewing for over an hour, stopped for a few and then this. Somehow the thread tension got messed up. I rethreaded and all is right with the world. I never have to adjust my tension though.

When the thread is going like that on the bottom - this means the top thread is your problem.... Try rethreading watching the the looper that goes up and down... that use to happen to me when I would sew and that thread would loop around the pull up threader ...

Well, I was having the same problem, plus my machine was eating my material. I finally figured it to be the bobbin. I had the wrong kind. Some machines are very touchy, so went to my machines booklet and got the bobbins number and bought 50 from ebay for 5.00. Now all is well. I had to rewind the old bobbins on to my new ones. I have two different machines with different bobbins, so marked my brother bobbins with marker red and pfaff blue. Am giving my other bobbins to someone else. Hope this helps.

Glad to hear that the suggestions worked! I have had the same problem with most of the machines I have or have had and when I do the things that have been listed above it usually works great..The last time I still had a problem and finally after going over the process again I found a thread that was hidden behind the tension disk..another time, another machine I found a small thread under the bobbin race..both of these looked like a tiny piece of lint and as I got a hold on them with a tweezer and pulled them out I found they were threads.. Happy sewing!!!