ubuntu 12.04 LTS hangs on boot when external monitor is connected

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http://askubuntu.com – I have a problem with my fresh installed Ubuntu 12.04 LTS on my Dell M4600: nVidia quadro 2000M i7-2860 16GB ram 128GB SSD Dell/Samsung 750GB HDD IPS RGB laptop display When it is connected via DP++ to the external Dell U2311H monitor, it hangs on boot or when wakening from suspend. If I detach the DP cable it boots normally. I have tried all combinations that I have found, as adding to grub: "no splash", "boot=pci", "acpi=off", etc... I have also changed in nVidia X settings that external monitor is the primary one and also tried to delete monitor.xml file. There is no change it ha (HowTos)