Otherwise, you need to remove and reinsert the battery to reset the camera. You should also verify that the battery is charged since a dead battery obviously will make the camera go offline. One way to test is to swap batteries around. If the battery is dead, a possible reason is the WiFi quality for that camera, whether signal strength or some 2.4GHz interference (WiFi or otherwise). Swapping cameras around will help nail down if it's a camera/battery issue or a position one.