Remove the back of the camera, point the lens towards something bright, and click the shutter: Do you see a flash of light through the back of the lens?
Oh by the way if you need to disassemble the camera, best not to forcibly unscrew the lens: IIRC, there's a small screw on the reverse side of the lens which acts as a stop. Be on the lookout for small loose parts, particularly springs which may have become dislodged. You may need to do some experimenting to figure out how to put it back together correctly, but there's really very little to these cameras.