Issue connecting HP Elitebook 840 G6 to a 4k Monitor. No video output

[isherpa]

Trying to connect a work issued HP Elitebook 840 G6 laptop to the BenQ PD3220U monitor using Thunderbolt, HDMI and Displayport (by way of the HP slim dock), but I'm not able to get the monitor working for this laptop. The cable i tried supported displayport 1.4, not the one supplied with the BenQ. The thunderbolt 3 and HDMI cables were from BenQ. Any thoughts on why I can't get video displayed on the monitor? 

[banhien]

@isherpa 

The specs of monitor is

        https://www.benq.com/en-au/monitor/designer/pd3220u/specifications.html

You should be able to use a  Thunderbolt cable to connect direct to your computer and you can daisy chain to a second monitor. You can use the slim dock to connect to other devices.

Regards.

[isherpa]

that's the problem I'm having - i'm not getting the video signal using a thunderbolt cable from laptop to monitor. also not working with HDMI. i also tried the laptop on a slim dock and used Displayport cable.