Phone enter only downloading mode.

Hello,

i have to repair an samsung a5 2017 lcd. The problem is that, the phone goes only in the “downloading mode”. So i disconnected the battery and when i ocnnect it again. The screen is black, if you charge it is black, if you connect the phone to the pc, the computer doesnt recognize the phone. The only thing you can do is hold the 3 buttons( power, volume down and home button) and it enter in this downloading mode, otherwise the screen remain black.

In this downloading mode, you have 2 options:

-volume up (contiou) , then it is stuck at downloading screen

-volume down, then the screen remain black.

I also tried with the samsung smart switch program but it doesnt recognize the device. It says that it is an ukniwn device.

Any idea how to solve this?