The max res of your laptop is 1920x1080. As far as I know, 30" does not support a 1920x1080 native res.
On my 30", the native res are 800x600, 1024x768, 1280x800, 1280x1024, 1600x1200, 1680x1050, 2400x600, 2492x600 and 2560x1600.
Hence, the "max" res on your 30" would be 1680x1050 or less since 1920x1080 is not supported by your 30".
Alternatively, right click on your desktop and select "screen resolution". Check what resolutions are available.
If 1280x800 is the max res, try updating your VGA drivers.