I feel your pain! Been there done that. If you removed the bobbin case to remove the lint go back and make absolutely sure that you put it back in 100% correctly. That was a problem for me more than once, it wasn't quite right. Then rethread both the bobbin and your upper thread to make sure that you have gone through the tension disks . I had to do that process a few times before I got it all correct. Take your time and good luck.