So I'm running KDE4.1 on OpenSUSE 10.3 on a Samsung Q45...

Yesterday, I decided to update the KDE install to the latest stable versions of 4.1; so I sought out the KDE4 packages, selected the latest versions from the KDE4:STABLE repo, and installed them. On rebooting, there was an ominous delay in the startup process after logging in, and then the system produced a blank grey screen. Curiously, the various system-tray K apps (kerry, klipper, kpowersave, kmix etc) all showed their icons briefly as they started up, just as normal.

Trying to start kde from the command line got a "$DISPLAY is not set or couldn't connect to the X server" error. Fortunately I was able to start work this morning in my KDE3.5.7 desktop, and to run Kontact/KDE4 under KDE3, but trying to fix the problem by the obvious route - revert the upgrades - lands me straight in Dependency Hell and seems to be actually impossible. Incredibly, YAST2 doesn't have an explicit "roll back last update" function..

I had a similar error after a Samsung BIOS update in January 2008, which resulted in me reinstalling KDE from scratch, and I never got my 3D desktop (I was then using Mandriva with Metisse) back.

Right; the problem was that I hadn't updated kdebase and kdelib.