[Help] Lg G3 randomely swithch off problem. topic

Hello;

My lg g3 has some strange and weird problems.

First it switch off randomely and does not switch back on normally, so i have to plug usb cable connected with charger or pc and then press power on button and then it turns on.

secondly it looses signals where as other phones have full signals at the same place with same carrier.

it was on stock 10R but then i decided to root it and install custom rom that might solve the problem, so i downgraded to 10C (since rooting 10R is bit difficult), rooted and now installing TWRP. but still problem is same.

so i think this has nothing to do with rom. Please help me to solve this issue. :(

Thanks