Hey, I just registered to this forum only to tell you my workaround for the problem with Windows 8 the minimum resolution width of 640 pixels:
As described previously you can circumvent the black display problem by rotating the screen into landscape mode (increases horizontal resolution of displays normally used in portrait mode) and pressing the win+d combination.
So I wrote a AutoIt script for myself which is activated via a shortcut, which quickly rotates my small portrait screen into landscape, presses win+d, rotates the screen back to portrait mode and restores all windows back by sending win+d again.
I just klick this shortcut after I turned the pc on and can use my 7" monitor without problems.
This does not solve the problem but enables you to live with it pretty well.
I used the following program in my script, which enables me to rotate only the second screen:
http://noeld.com/programs.asp?cat=misc#display
My script looks as follows:
Run("C:\display.exe /device 2 /rotate 0")
Sleep(1000*2)
Send("#d")
Run("C:\display.exe /device 2 /rotate 90")
Sleep(1000*2)
Send("#d")