After sewing a zigzag stitch it will not sew a...

Question

brother project runway limited edition ce-5000prwsewed binding on a blanket with a zigzag stitch tried to sew a regular stitch and the bobbin tread keeps tangleing and bunching up.Have taken the bobbin assembly apart same bobbin that we where zigzagging with. changed it out with a new one anyway. tried going back down thru the stitches from zigzag to reg. still will not sew a reg. stitch. It is less than 6 weeks old