Displayport 2560 x 1440 not working on Elitebook 840 G3

[roddyc]

I have 2 new Elitebook 840 G3 laptops.

They came with windows 7 out of the box, and I upgraded one to Windows 10 64bit.

I have the same problem with both.

Neither will display anything over displayport to a BenQ BL3200PT AMVA+ 32-inch Monitor 16:9, 2560 x 1440.

The laptop is advertised with:

"DisplayPort Supports resolutions up to 4096 x 2160 @ 60 Hz Resolutions are dependent upon monitor capability, and resolution and color depth setting"

When I plug in the cable, the laptop screen goes blank, the monitor just turns off with no signal.

To get the laptop screen back I need to unplug the cable, and sometimes actually plug it back in.

Shutting down with the cable plugged in ends with an incomplete shutdown, and needs the power button held down until the lights go off.

The same monitor works fine at full resolution with a USB>DisplayPort displaylink adapter. So, the cable+monitor appear to work fine.

I've gone into the bios, and increased the video memory to 512mb, but that hasn't made a difference.

I've switched down from displayport 1.2 to 1.1 compatibility in the monitor settings but that hasn't helped.

I've used SoftPAQ to go to latest bios, video drivers, chipset drivers.

I've uninstalled HP video drivers and gone with newer intel native drivers. Exact same behaviour.

So, the fact that this is happening on two laptops strikes me as strange. It's hardly a hardware problem.

I don't have a 2nd displayport monitor, so I haven't tried that. 

Has anyone any ideas?

update 9-Jun-2016:

I tried the elitebook with a ProDisplay P242va1920x1080, and that worked perfectly.

So, it's either the resolution, or a specific problem talking to the BENQ.

[roddyc · Accepted solution]

After some searching, it appears that other people have had issues with the BENQ using displayport.

I tried the suggested "fix", which is to do a hard reset using the on-off switch on the back of the monitor.

This solved the problem, and the monitor immediately started working.

Unfortunately, it sounds like this is something that has to be done regularly, and BENQ don't have a fix for it.

So, not a problem with the Elitebook at all.