Comment 6 for bug 182288

I've experienced almost the same things as Mr. Wep. I've got a Nvidia 7600GS, and using the nvidia module from nvidia-glx-new package. According to the Xorg log everything is fine, but when I set SystemSettings/Desktop/DesktopEffects/AdvancedOptions/CompositionType from XRender to OpenGL, the whole screen gets black, and the system behaves just as Mr. Wep described. So now I'm using kde4 without the desktop effects.

some additional information:
Hardy kubuntu kde4 edition

lspci | grep VGA
01:00.0 VGA compatible controller: nVidia Corporation G73 [GeForce 7600 GS] (rev a2)

xdpyinfo | grep Composite
Composite

Glx extension works fine as well.

Peter