I have a problem in ubuntu 12.04 with my Dell M4600: nVidia quadro 2000M, i7-2860 16GB ram, 128GB SSD Dell/Samsung, 750GB HDD and IPS RGB laptop display. When it is connected via DP++ to external Dell U2311H monitor it hangs on boot or at wake from suspend. If I detached 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 hangs each time.
It starts to load deamons then both screens are blank and then completely hangs with beep sound.

What I discovered is if I detach cable wait 2 sec after grub starts booting and then physically connect DP cable while the ubuntu still booting everything works normally and I have picture on my external screen while the laptop screen is off, just as I wanted.
Do you maybe know how to solve this issue. Thank You.