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i'm trying to connect an external monitor to my Lenovo T420 using the DisplayPort but it's not working. If i connect it via VGA it works fine, but the image on the monitor is lacking sharpness and it's flickering (the cause of that I discovered to be some interference in the VGA output). So, I want to connect my external monitor using DisplayPort, but when i do so, i get no image on it. And when i run the xrandr command, I don't see any display port:

    $ xrandr
Screen 0: minimum 320 x 200, current 3520 x 1200, maximum 32767 x 32767
LVDS1 connected 1600x900+0+300 (normal left inverted right x axis y axis) 309mm x 174mm
   1600x900       60.0*+   40.0  
   1440x900       59.9  
   1360x768       59.8     60.0  
   1152x864       60.0  
   1024x768       60.0  
   800x600        60.3     56.2  
   640x480        59.9  
VGA1 connected 1920x1200+1600+0 (normal left inverted right x axis y axis) 518mm x 324mm
   1920x1200      60.0*+
   1920x1080      59.9  
   1600x1200      60.0  
   1680x1050      60.0  
   1280x1024      75.0     72.0     60.0  
   1440x900       75.0     59.9  
   1024x768       75.1     70.1     60.0  
   800x600        72.2     75.0     60.3  
   640x480        72.8     75.0     66.0     60.0  


When running lspci -v i can see both my graphic cards:

00:02.0 VGA compatible controller: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller (rev 09) (prog-if 00 [VGA controller])
    Subsystem: Lenovo Device 21d0
    Flags: bus master, fast devsel, latency 0, IRQ 46
    Memory at f1400000 (64-bit, non-prefetchable) [size=4M]
    Memory at e0000000 (64-bit, prefetchable) [size=256M]
    I/O ports at 6000 [size=64]
    Expansion ROM at <unassigned> [disabled]
    Capabilities: <access denied>
    Kernel driver in use: i915


01:00.0 VGA compatible controller: NVIDIA Corporation GF119M [Quadro NVS 4200M] (rev a1) (prog-if 00 [VGA controller])
    Subsystem: Lenovo Device 21d0
    Flags: fast devsel, IRQ 11
    Memory at f0000000 (32-bit, non-prefetchable) [disabled] [size=16M]
    Memory at c0000000 (64-bit, prefetchable) [disabled] [size=256M]
    Memory at d0000000 (64-bit, prefetchable) [disabled] [size=32M]
    I/O ports at 5000 [disabled] [size=128]
    Expansion ROM at f1000000 [disabled] [size=512K]
    Capabilities: <access denied>

In Bios my settings are "Discrete Graphics" and OS detection Disabled. Any idea what i could do to make the display port work?

I'm running Ubuntu 13.04.


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