My best guess is breaking thread may be an issue with how it is threaded...

After you thread it and the presser foot is up, can you pull the thread easily? How about the bobbin thread, can you pull it easily? If not, then there's a problem with how it's threaded and that's why it's breaking.

You may have a burr in the needle hole of the cover plate, or on the bobbin shuttle--you can feel it with your finger--buff it with emery. Sometimes the needle hole has a burr, Have you changed needles? Always thread with the foot up, and as above suggested, raise to test the tension. If the thread comes easily with the foot down, tighten--but raise the foot when you tighten. Then test again. If it is too loose, it will 'flop' and hang up and break. You may have just missed a step in threading.

try this link for a free manual from singer website
they might have a free manual

Here is a link that might be useful: http://www.singerco.com/accessories/instruction-manuals

turn your thread over - sometimes it hooks on the little slot

The top thread breaks
1. the needle thread is not threaded properly
2. The needle thread tension is to tight
3. The needle is bent or blunt
4. The needle is incorrectly inserted
5. The needle thread & the bobbin thread are not set under the presser foot when starting to sew
6. the threads were not drawn to the rear after sewing
7. The thread is either to heavy or to fine for the needle
8. Try a different spool or cone of thread

This is going to sound goofy: How old is the thread?

I had a spool of thread that broke every few inches. I thought it looked dusty on top, but when I tried to brush it off, I saw it was faded. It broke on the faded part, every time.

Do you ever take the throat plate off and clean around the feed dogs? Lint builds up under there and will cause thread breaks. Take some canned air and blow it out. Hope that works for you! :-)