After my system drive failed, I reinstalled Debian 12 with KDE and kept my personal data on a separate drive. Logging in through SDDM works, but KDE displays a black screen immediately afterward. Using nomodeset allows the desktop to start, which made me suspect leftover user or Plasma configuration. I reset the KDE settings and eventually replaced the contents of my home directory with a fresh default setup, which temporarily fixed the problem.
The issue returned after launching an older Windows game through Wine. After a forced shutdown, changing the monitor from one HDMI port to another temporarily restored the display, but I had to repeat that after every boot. Restarting SDDM seems to have left me with a black screen again. I can still switch to a TTY, and nomodeset restores the graphical session. The login screen itself always appears normally, and I am using an X11 session.
I would like to completely reset the relevant KDE, display, graphics, and desktop configuration or otherwise identify what is causing the session to fail, without reinstalling everything or losing the work I have done. What should I check or reset from a TTY?
1 Answer
Create a separate test user and try logging in with that account. A new user starts with clean home-directory settings, so this helps determine whether the problem is limited to your existing KDE configuration or affects the system-wide graphics setup. Since SDDM and the login screen work, the failure may be happening when Plasma starts. You can create the account from a TTY with a command such as `sudo adduser testuser`, then log in through SDDM and compare the result.
The login screen works normally, but the display goes black after I enter my password and the KDE startup animation finishes. I am using X11. Should I create the test account from the TTY, or can it be done from the login screen?