Tu as bien la version avec le chipset intel et pas nvidia ?
Alors c'est marrant c'est la résolution max. de ton écran quant tu branches un écran externe dixit le site de dell.
Note: If you connect an external display that cannot scale to the resolution of the internal LCD (1366 x 768 or 1600 x 900), if you clone the displays, the internal LCD will scale to the lower resolution of the external display (EXAMPLE: 1024 x 768), 1200 x 800). If the external display is a higher resolution than the internal LCD, the external display should scale to the internal display resolution in a clone mode.
If you extend the desktop, the optimal resolution for each display should be displayed (EXAMPLES:1920 x 1200, 1680 x 1050, 1440 x 990) unless you displays native resolution exceeds that port capability of the video port. (E-Port DVI connections are limited to 1920 x 1200 for example.)
In all resolutions below 1920 x 1200 the limiting factor for display resolutionis normally the display capability of the display you have connected to the dock. Older or economy displays may not have high resolution capabilities od 1920 x 1200 or higher.