Help me plz ! about DVI-ADD2 and ACD20"

[Amethyst]

I connect my 20" Apple Cinema Display with my computer by DVI port (with GMA900 and SIIG DVI-ADD2N Cards). After I turn on the power and wait for my computer boots OSX, my display doesn't work, it only show blink "_"

 

On the other hand, I connect my computer with 17" Phillips Display by VGA port. After I turn on the power and wait for my computer boots OSX, my display work (it's show OSX screen).

 

Now, this time I let my computer boots OSX, and show the osx screen. Afer that, I take out my 17" Phillips Display that connect by VGA port, I connect 20" Apple Cinema Display by DVI port again. This time it works. and get optimum resolution (1680 x 1050)

 

The question is

 

How can I make my 20" Apple Cinema Display work if I connect it before I turn on my computer? because I don't want to connect 17" Phillips and wait until it's show osx screen , then take 17" Phillips out and connect 20" Apple Cinema Display every time I use it.

 

Thank you very much

 

 

my configurations:

Intel Pentium 4 630 3.0Ghz

MSI 915G Combo-FR

Intel GMA 900 Onboard

SIIG Orion DVI-ADD2 N Cards

Dual Channel DDRII 2*1 GB

Apple Cinema Display 20"

Mac OSX 10.4.5