What makes the bobbin thread skip, break, and keep sewing? I have adjusted the tension up and down, and nothing works. I have also changed the needle, re-threaded it and taken the feeder apart, etc.

Have you oiled your machine? If not, remove the needle and foot. Take the bobbin housing apart, and remove the top cover where the light is, and brush it out with a small brush. Drip a few drops of machine oil onto a soft washcloth and wipe down the inside of the bobbin housing and the shafts in the top part. Put 2-3 drops of oil where specified in your manual. Run the machine at full speed for about 45 seconds. Put it all back together, and it should work great! Also, make sure you are using quality thread, as cheap thread will clog up your machine.