29" Ascension mountain bike by Schwinn My freewheel stopped working. I can still pedal forward, but not backward. What's wrong with it?
If you have a freewheel (which it seems like you have on the BSO), and theres anything wrong with it, the solution is to replace it (if those directions don't work, you can try this method). In general, they're not user serviceable parts.

My guess is that you have some pawls stuck or something.  A stopgap measure that might work is dumping wd-40 or similar into/around the freewheel.

In any case, the repair will be the same -- buy a new freewheel, a freewheel remover tool and install a new freewheel on.