Broke Kubuntu a little — wanted to enable window manager effects. Turned them on — laggy. Decided to install drivers. The native Catalyst refused to install — it didn’t like the OS version. Installed what was in the repos — Kwin started crashing. Windows without title bars look quite funny :) And the keyboard stopped working, only the mouse. Found an article (the text is quoted below, link: http://www.kubuntu.ru/node/3201), used it to fix things (removed the driver).
Moral: don’t buy ATI video cards, kids.
Here’s the solution to the problem that was causing KWin to crash for me. As it turned out, it was all because of the downloaded ATI driver for the GPU — I just missed that moment because I downloaded everything together with various updates. Luckily there was someone nearby who helped figure out what was going on. We analyzed the logs in /var/log/Xorg.0.log and kdm.log
Once we figured out the driver was to blame, we decided to remove it. Sequence of steps: Alt+F1 (console), log in, sudo su. dpkg -S libglx.so — to see what to remove; I had fglrx-something-something… apt-get remove fglrx-something (put your own driver name here) rm -rf /etc/X11/xorg.conf restart KDE manually /etc/init.d/kdm restart or just reboot KDE should start with the default video driver.