U4320Q, black screen when ON

Hi guys. Does anyone know how to fix Dell U4320Q monitor? It always shows black screen. the only i can adjust is brightness of a backlight. Can't perform trouble shooting or factory reset from monitor itself as menu doesn't show up as well. The other interesting thing - if any laptop connected to it at first time it mirrors screen for a moment then get back to black one. Maybe there is some tools for factory reset, which you can suggest me to use? Can it be firmware issue? Appreciate your help.