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See the screenshot below. It shows the Windows display properties in German. I can configure a second display, although I have not connected one. So far, so good. Only it does not work: When I click on OK, then the screen flashes, but nothing changes, and the option "Windows-Desktop auf diesen Monitor erweitern" ("Extend my Windows desktop onto this monitor.") is unticked.

How do I make Windows believe that there is a second monitor? (ATI Radeon Mobility 9000)

Why I want to do this? I want to access the second screen via VNC from another computer.

Windows display properties in German

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I've read your answer, question, and the "similar" question. But is there another "universal" way to do it? Because I've no ATI/NVidia graphics adapter. – Searush Feb 18 '13 at 13:32
@SEARAS Judging from the solution, I assume this is a driver thing. So, my suggestion is that you create another question, mentioning your graphics adapter. In fact, I just updated my question to make it specific to the adapter in my laptop. – feklee Feb 18 '13 at 13:44

Inspired by an answer to a similar question, I found the solution. In the graphics adapater's advanced settings, ATI CATALYST Control Center, there is an option to force "detection" of external TVs. It is the option "TV-Erkennung erzwingen" in the screen shot below.

Although my intention is not to connect a TV, this does the trick.

CATALYST Control Center

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