Today, I couldn't manage to log in at all, also not with the Ctrl-Alt-F1 startkde workaround, I tried a view things, an older kernel that was installed, but that didn't help. What finally worked was to use the "(upstart)" version of the current linux kernel available via grub. This produced the lightdm login and then I could do the Ctrl-Alt-F1 startkde workaround. From there, I upgraded to 15.10. Now I'm back to the original problem. lightdm login comes up, logging in doesn't work, the Ctrl-Alt-F1 startkde workaround works.
Today, I couldn't manage to log in at all, also not with the Ctrl-Alt-F1 startkde workaround, I tried a view things, an older kernel that was installed, but that didn't help. What finally worked was to use the "(upstart)" version of the current linux kernel available via grub. This produced the lightdm login and then I could do the Ctrl-Alt-F1 startkde workaround. From there, I upgraded to 15.10. Now I'm back to the original problem. lightdm login comes up, logging in doesn't work, the Ctrl-Alt-F1 startkde workaround works.