cannot connect to X server

Hi,

I know this is common question, but I can’t figure out how to fix it !

I’m connected to my beaglebone black with a serial cable and I would like to start a gtk application.

My problem, is that I’ve the error message : “cannot connect to X server” …

I’m on the distribution Ubuntu, with only the console running and lxde… The screen is not calibrate, so I can’t go on the menu of LXDE and choose in the option calibrate screen …

When I want to start manually the calibration, I’ve this error message :

xinput_calibrator --list

Unable to connect to X server

I’m Totally LOST, I don’t know what to do, where to go …

Ok,

I manage something new, I started lxde with startx & and then I start my gtk application. The window show up, that great, but I got as an error =>

Xlib: extension “RANDR” missing on display “:0”.