First of all, sorry for my english, I'm from Germany.
No option of dual-graphics appears in Catalyst (updatet version). I have an R7 270x 2gb. If i plug in hdmi cable (connection to a led-tv with potion as an monitor) my PC monitor doesn't work, only shows the wallpaper and no mouse or applications, statusbar..... this is only on the tv screen. What's my mistake?
Normal multi-monitor setup exists in two modes - extended desktop and clone. If you're trying to show the same image on both displays, you want clone mode.
Open Catalyst Control Center (right click on empty desktop space), click Desktop Management, then click Creating and Arranging Desktops. The one with the asterisk is set as primary. You can click the downward arrow on the other to select Make Primary, which will swap them. In the area blow, with the smaller monitor images, click on the downward arrow to open the menu, then select Duplicate to convert the secondary monitor to Clone.