Before you scream at me for using VGA, this is not my primary machine I am using. I need a display for an old Mac Mini and don't want another monitor. Anyway, I was trying to connect using the DVI port on the back of a 2006 Mac Mini (one with white top), and a DVI to VGA adapter. I get an error whenever I switch to the D-Sub input, I get an error saying "Out of range", and then blue is the only color to appear. I can see the interface in a really glitchy manner, in probably what is 800x600, but it is unbearable. To save you some research if you didn't know already, the XL2420TX is a 1080p 120Hz monitor. It works fine with DVI and HDMI. Have had no problems with this monitor except this. My guess is that it Snow Leopard (what I am running on it) doesn't support this kind of display, but I could be completely wrong. Any help?
Are you sure the pins on the male connector isn't damaged?
Did another discovery as well. VGA only supports uo to 70Hz. So if your monitor or settings on OSX is amping the VGA connection I suggest you try to lower the RR to said maximum support.
Snow Leopard is BSD right, there must be a way to manually set the mode in terminal. Normally this would be done by calculating the VESA codes for the desired setting. It should be possible.