", it will not work with flashlight apps "
That means it likely needs repair. You can try a full reset (I'll defer to the web on that) but it seems "used" so I'm unsure what warranty you have. Repair of such phones usually cost more than a new phone so get a price and decide.
I bought an old Galaxy S2 today. Everything is fine, except Camera flash
sometimes it stop working. Sometimes it works but the captured images are totally black even though camera flashlight are fired.
I Downloaded flashlight app and check. It works fine, but if flash stopped working on Camera, it will not work with flashlight apps also,
I followed some guys' step, they said that Camera app's data then remove battery and turn on phone again, It just worked sometimes
So, is it problem with camera hardware or firmware, can you give me any solution?
I'm using android 4.1 version