Black screen after login Kubuntu 15.04

I ended up having to rename ~/.kde, ~/.cache ~/.local and ~/.config.

mv ~/.kde ~/.kde.old
mv ~/.cache ~/.cache.old
mv ~/.local ~/.local.old
mv ~/.config ~/.config.old
shutdown -r now

Not sure exactly which one did the trick but I suspect it was .config.

This has troubled me for some time now. I noticed it happens when I put Kubuntu to sleep or shut it down with a dual monitor set-up and then trying to start it with the laptop screen only. Anyway, here's what I found - one particular folder is responsible for this mess. Deleting it fixes my problem.

Here's what to do. Once you get the black screen go to a tty (Ctrl+Alt+F1) and do the following:

 rm ~/.local/share/kscreen
 sudo killall sddm

Then enter your password and login. Everything should be ok. Hope this helps ;)

I may have a solution, I've been trying to figure out what happened for a few days now. Deleting all ~/.cache and ~/.config is not a great idea, as those could be needed but. . .

In ~/.cache, I have deleted only the files with a 14.04 boot DVD, but I have kept the folders:

activityswitcher_wallpaper_preview.kcache
event-sound-cache.tdb.093cbe7e51f0423cb8a1384115f450a1.x86_64-pc-linux-gnu
icon-cache.kcache
ksycoca5
ksycoca5stamp
motd.legal-displayed (0 kb)
plasma-svgelements-air_v1.0
plasma-svgelements-breeze-dark_v0.9.7
plasma_theme_breeze-dark_v0.9.7.kcache
[...]
plasma_wallpaper_preview.kcache

After rebooting, the desktop was fine.