BOBBIN THREAD. I HAVE A BROTHER XL-3100 SEWING MACHINE, IT WORKS FINE SOMETIME, OTHER TIMES, I

Question

I HAVE A BROTHER XL-3100 SEWING MACHINE, IT WORKS FINE SOMETIME, OTHER TIMES, I WILL BE SEWING ALONG AND ALL OF A SUDDEN IT GETS HUNG UP AND THE BOBBIN THREAD EITHER BREAKS OR SKIPS, OR IT JUST WONT MOVE WHEN I PRESS ON THE FOOT PEDDLE....HELP.PLEEZ
THANX