Hello, my screen stays black when I push the power button of my Samsung Galaxy A40 since yesterday. I have this phone about 2,5 years.

When I tried to activate my phone, the screen stayed black so I went to charge it because I thought the battery must be empty.
When I plugged it in, it gave a sound, which means it was connected.
After 1 hour of charging I tried to use my phone, but the screen stays black.

I then tried to force reboot it pressing the Volume down and Power button simultaneously.
It vibrated so this combination still works, so I think it worked, but again, I see nothing on my screen.
Then I try to restart it by pressing the power button. The phone gives me sound and vibrates when I push the screen when I should enter the code to start it up, but the screen stays black.
Yesterday evening the screen lighted up suddenly when I pressed the power button, I entered the code, everything started up as normal, I thought it would be fixed.
But when the phone went back to sleep, the screen stays black when I try to activate it again.

My phone did not get wet or fell on the ground or anything, this problem came out of nowhere.
Any suggestion on what I can do? Thanks in advance.