No display manager launching

[gogor44]

I just installed debian 10, and it gives a black screen. There are 3 graphic manager installed above, when I launch with sddm it opens a black screen and directly requests the user’s loigin and pqssword, when it’s in gdm3 or in lightdm it gives a black screen with a cursor which blinks and you cannot do anything with, when I do alt + f1 it returns to a screen where you see the history of actions and where you can enter the login and the password.
I have tried

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apt-get update

,

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apt-get upgrade

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apt-get install grub

, I went to

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/etc/apt/soiurce.lists

I added

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contrib non-free

after the source lines, then installed

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firmware-linux

I did updates and upgrades, I went to grub I replaced

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quiet

by

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nomodeset

then I reset

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quiet

by doing

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update-grub

after each change and

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reboot

in when it had a chance to be useful.

No result

The video card is a radeon vega graphics

Thank you for your help.

[Head_on_a_Stick]

http://forums.debian.net/viewtopic.php?p=716363#p716363

Please search the boards before posting, I wrote that reply just a few hours ago so you really should have seen it.

[gogor44]

I am sorry. As you could guess from the actions that i have enumerate, I had done some researches before posting, it was in vain, and then I left to cry, when I came back after my depression I couldn't guess that there would be someone who encountered the same problem as me during the time when I had abandoned my researches.
If you want I can remove this post and continue to asking my questions under the one you have mentioned.
Now I have done what you described in the other posts. I have upgraded the kernel, and I have re-downloaded the non free firmware, it didn't work, I have downloaded the firmware from the git repository that you mentioned with updating and upgrading whatever was possible. It still not work...
And yeah, it was working correctly with ubuntu 18 lts that i had installed in September 2019 so are the newest Debian firmware older than the firmware of ubuntu from Septemper 2019?

Edited: I have actually remarked that the last displayed instruction before the terminal screen appearing, is something with "firmware error" but it desperate too fast so I don't have te time to read the exact line.

Edited: Actually that was about the wifi adapter firmware so that have nothing to do with the problem

[Head_on_a_Stick]

If you want me to help then I need to know your hardware.

Read the other thread, I've discussed the firmware there.