1. Is the needle bent? You've already tried another?
2 - Is the needle seated up as high as possible in the needlebar? Is it screwed in very tightly?
3 - Is the needle a sharp or ball-point and not one of the Singer "stretch" needles? (stretch refers to the needle, not to the fabric it is supposed to sew.)
4 - Is the needle positively the correct one for your machine? Some machines require different needles than the standard 15x1.