in most cases you camera port might be damaged or the camera module or there can be problems with the software also like denied permissions

might be a problem with the on/off strip please change it and if still same problem happens then try changing the battery and even after this the problem still remains then you have check for circuit shorts in the mobile circut propably near the power ic

go to settings and check for sim settings and from there select your sim and then if you check you can see a setting called preferred network go there and select the required network option