After logging into my account, I am presented with a black screen and cursor for around 3 seconds, after which it simply returns to the login prompt. I am on kde-unstable but I doubt this is the cause of the problem.
To clarify, this only occurs on MY account. Logging into tty3 as root and running startx works just fine and presents me with a desktop.
Status update: I can get into my account now by going into tty3 and then running startx, and then when it throws an error about the lockfile, I can hit Ctrl+C to stop it, and that seems to let me back into my account. It would seem that there is a problem with my account’s desktop/taskbar/wallpaper config as when logged in via tty3, it looks completely stock, no custom wallpaper or taskbar, nothing.
Did you check or is this a guess/feeling?