You might also start with a newly threaded bobbin. Did you by chance use a different spool of thread for the bobbin than you have for the top? I've had this happen to me a couple of times and I started with a new bobin and it actually worked. Don't ask why I don't know, but I had rethreaded and everything, then changed bobbins and BINGO. Like someone else said at least the ripping out will be quite easy. Good luck. Let us know, how things come out.