I had to reinstall Debian 12 with KDE after my system drive failed. My personal data was preserved on a separate drive, which I configured as /home. Since then, KDE sometimes gives me a black screen immediately after login. The display manager works normally, and I can enter a TTY, but after entering my password the KDE startup animation appears briefly and then the screen goes black. I am using an X11 session.
Booting with nomodeset restores the desktop, so I suspect a graphics or display configuration problem. I tried resetting KDE Plasma settings and removing old configuration files, and temporarily copying the default home directory contents made the desktop work again. However, after launching an older game through Wine, the screen went black again and I had to force a shutdown. Changing the monitor from one HDMI port to another sometimes restored the image, but now restarting SDDM has left me without a display unless I use nomodeset.
I can still access a TTY while the graphical session is black. What is the best way to diagnose this and reset the relevant KDE, display, graphics, and user-session configuration without reinstalling everything? Would creating a fresh user help determine whether the problem is limited to my existing home directory, and can that be done from a TTY?
1 Answer
Since the login screen works, first create a temporary user from a TTY and test a clean KDE session. Press Ctrl+Alt+F3, log in, then run `sudo adduser testuser` and follow the prompts. Log out of the TTY and try logging in as that user.
If the new account works normally, the graphics stack is probably fine and the problem is in your existing home directory. Do not delete everything immediately; move the suspected configuration directories out of the way so they can be restored if needed. For KDE and Plasma, start with directories such as `~/.config`, `~/.local/share`, and `~/.cache`, or rename them one at a time while logged out. Also check Wine and game-related configuration separately, since the crash may have changed display settings or triggered a GPU driver issue.
If the fresh account also shows a black screen, the issue is more likely related to the GPU driver, X11 configuration, monitor connection, or kernel rather than KDE’s user settings. Collect the graphics hardware and driver information, then inspect the previous boot and X11/SDDM logs from the TTY instead of repeatedly forcing shutdowns.
The login screen itself is always visible, and the black screen begins right after I enter my password. I will create the test account from a TTY and compare the results. I am using an X11 session, not Wayland.