Problem with KDE logout

Hi, I have change my hard disk so I reintall my system, my old disk
go to my girl PC so I also reinstalled it. both PC have openSUSE 12.1
x86_64 KDE4 from the oss repo and privative nvidia or ATI driver, and a
clean home directory… the problem is that sometimes when I try to
logout, reboot or shutdown (hotkey or menu option) the system only close
all apps and slow the screen bright and the only way is to use a terminal