Why does my seeing machine keep unthreading the needle as I am sewing?
Two possible reasons. One, your needle thread comes out before you begin because it's short and needs to be held when you start. The other is, you may have a small snag in your needle eye and it cuts it. The next time it happens, look at the end of the thread. If it look somewhat chewed...it's that. I hope this helps.
There are several reasons your sewing machine needle won't stay threaded, starting with the needle (as noted by the previous poster) is old and going through reasons like:
Wrong needle for the type of thread and fabric you are trying to sew
Upper thread not put through the machine threading path correctly
Machine tension set incorrectly for the type of thread, needle, and fabric you are using
Bobbin gear worn or broken (which prevents the upper thread from being caught by the bobbin during sewing)
Best solution? Check your user guide (aka owner's manual) troubleshooting pages. If you don't have your user guide, check the manufacture website, most have a free download feature for user guides. Print the guide and put it into a 3 ring binder to have at hand during a sewing session.