IT issue - connecting a third monitor

I have a HP elitebook and a HP port. I have 3 external monitors connected to the laptop.

The new monitor was added this morning but the laptop refuses to run 4 screens, although they are all acknowledged and working... only 3 can be run at any time. At the moment I've got the laptop screen on.

The internet tells me that the elitebook will support 4 screens.

2 are connected with D cables, 1 with an HDMI, all 3 additional monitors are connected straight into the port.

Any ideas how to make the laptop happy with 4 screens at once, all are acknowledged and all work... just not together....?

I think there can be an issue with high resolution monitors, at least there is with thinkpad's. How old is your laptop? I assume your display port ones are going through some type of adaptor as I doubt any laptop has 2 displayport as well as an HDMI. If it is one adaptor for two monitors try splitting them between the USB ports if you have another one handy. Also try a cheapo multi-port adaptor e.g. MOKIN.

If it is all work stuff they should get it working for you?

What's a D cable? do you mean USB-C/Thunderbolt, or DisplayPort?

Are you sure it should work - a lot of Intel integrated graphics processors are capped at 3 displays.

Four monitors is going to push you into marginal areas of weirdness with the standards. e.g. I'm pretty sure Thunderbolt controllers only support two display outputs each, so you'd need some way of parsing a single display output into two. Some fancy docks can do that - search for MST docks.

If any of the monitors have pass-through you could try daisy-chaining two of them as well, might work.

Try plugging one of the cables directly into the laptop while the other two are plugged into the docking station.

I have an older Elitebook that says it supports three external monitors, but through the dock it only supports two. The third has to be plugged directly into the laptop's HDMI port.