I have some problems in kde which appear without any obvious reason.
Suddently kdesu doesn't work. When I try to run a program, after I input my password I get the error that su doesn't found , ensure that the path is setup correctly(translated from greek).
Also when I'm trying to open konsole to start it from there, konslole opens and hangs. The cursor doesn't flash and I cannot write anything.
Both worked fine before today and I didn't update or install something before this start happens.

And I had sometimes again strange freezes when trying to input my pass on kdesu prompt or when tried to logout from kde.

And one more issue(this is probably related to my graphics card driver) is that when I logout from kde, instead of kdm, appears a black screen with mouse cursor which work though. In fact kdm works but I cannot see it. If I input my pass, kde starts again.
I found that is related to desktop effects engine. Happens when I have Opengl. I thought that solved when I installed the closed source ATI driver, but now appears again. It worked fine for a couple of days though, but suddenly stopped working.

Any help/solution on any of these?

EDIT:
kdesu issue seems that was related to gnome-session, when I uninstalled it start to work as normally egain.
konslole too..
seems that kdm problem solved also..

Could you mark the problem as solved in the title, then? Thanks.