How can I fix my New Home sewing machine?

Suddenly ceased to form stitches, following my change of straight stitching to zig-zag, during the process of sewing a 3 width curtain. Thread became tangled in the bobbin and the needle jammed. Having freed the needle and bobbin and reset machine to straight stitching again (and oiled the shuttle), the same problem remains. Any suggestions for remedying this please? PS Needle is correctly placed, bobbin correctly threaded and machine correctly threaded also.