Pixhawk 2.4.8 has no connection with computer

My computer doesnt even see pixhawk 2.4.8 . I never saw white light on pixhawk until this day. There is a white light that doesnt blink also when I connect my computer with pixhawk, there is even no sound. No idea what is the problem. Can anyone help me about it ?

Update to the latest mission Planner, and try a diferent USB cable.

I tried both, also I tried with many computers. But there is no connection sound with pixhawk. Cant see anything on device manager.