I want to extend my desktop to an 2nd monitor. I have the monitor connected to the mac through the VGA with the Thunderbolt adapter. The mac recognizes the monitor (Acer S211HL). I've used the mirror function and every resolution and speed combo but still get no display on the 2nd monitor. The Acer was being used on an HP desktop until I got a new one. Do I need to buy a new monitor specifically for the mac? Any help is greatly appreciated.