Apparently, the monitor installed in certain circumstances, in addition to as "second monitor". Then I argue, even the second monitor when you turn the monitor and has him again until switching off / on for it to work normally. Is it in standby, I hear constantly the "Device added" / "Device Disconnected" signal of Windows. In the supplied replacement device that is the same way.
When I connect the PC to a different monitor everything works without problems ... Even with my new monitor from another manufacturer I am now fully satisfied and have no more problems.