Logoff and Login destroys desktop

Using Logoff of the Start Menu kills the desktop background, moving the [ALT][STRG][ENTF]-Window on the Screen (ENTF might be DEL on english keyboards) leaves the image of the window on that point it was, but the real window is where I dragged it. When I log in again, the taskbar is not reset or something like that, it is not there, and the explorer is opened. When I drag and drop this explorer window it leaves images of itself too. No taskbar, no nothing.