OS : ubuntu 12.04.2 LTS
OS Arch. : X86_64
Graphic : Nvidia NVS 3100M
External Monitor : Samsung SyncMaster S20R315B Plus
Laptop Model : DELL Latitude E6410
today I bought "Samsung Sync-master S20R315B" LED monitor. before power on machine, I plugged monitor cable in, then power on my laptop.
Ubuntu started without problem, but, when logged in Ubuntu, a window without title appear and its height is too tall , so i can't capture it better than this:

when ubuntu start nothing show in samsung monitor, well, so i run nvidia-setting command and and in the "X server display configuration" section, i see the samsung is disabled!
i have unplugged the cable and plug in again and now, laptop monitor is turned off and samsung showing desktop. it's good, but, if i unplug the cable again, laptop monitor don't show anything and remain blank!
i show you the configurations:
- Laptop :

External Monitor :

NOTE:
i'm beginner in ubuntu world, if you want any hardware information please explain what command should i run for it. :) thanks.P.S. now when i closed nvidia setting window, i see this error in terminal :
ERROR: Unable to open file '/home/netmoon/.nvidia-settings-rc' for writing.