plugging in external monitor to ubuntu 12.04.2 LTS causes unknown error at start-up

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http://askubuntu.com – 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 configura (HowTos)