As frustrating as it can be to have your sewing machine stage a revolt, the solution is likely quite simple. Downward pressure on the presser foot holds the fabric between the feed dog and sewing machine foot. It gets used once a year. Just because the tangled mess is on the bobbin side of the stitching, don't assume the fault lies with the bobbin. A massive nest of tangled thread is usually a result of the sewing machine being improperly threaded. It has no response from the air foot pedal. I have the same issue on my Singer sewing machine right now. My presser foot is stuck down and you can't flit the level to move it up. The amount of pressure would need to vary if you were switching between lightweight sheer fabric and multiple layers of denim for the machine to feed the fabric evenly. I had an old Singer sewing machine Model 6233 (1986). I did checked the small air pump inside and the tube. To correct this problem, put the presser foot up and unthread the sewing machine entirely. It worked well until today. Is it something wrong with the air pump inside or the problem of the foot pedal? This is an issue inside the machine and I had to take mine to a repair shop in order to have it fixed. If your presser foot pressure is correct, and your feed dogs are working properly, try switching to a walking foot, which can help even out the feed for slippery or heavyweight fabrics. Or will a broken foot pedal will make it stop working?