X301 displayport no video

[vaggs]

Hi all, sorry if this has been asked before but after a quick search I didn't find something.
I'm trying to connect my X301 to a Dell 3008 via the displayport.
The moment I connect the cable on the tp the display goes to power saving mode.
I have the latest updates from lenovo. using Intel Graphics and Media Control Panel I can see that the external display has been detected and the resolution correctly set.
However, the external display is blank.
Any suggestions?