Why is the boot sequence no more visible with a Gainward GTX 1060 Phoenix?

Question

I have a Gigabyte GA-Z87MX-D3H with a Xeon E3-1230 v3 and a Dell UP2414Q set to use DP 1.2a to get 4K@60 Hz via DisplaPort.

With a nVidia GTX 760 the monitor was turning on at boot, in time for me to see the Award logo and to enter the UEFI BIOS. The BIOS is set to "other OS" (vs Windows 8) and secure boot is disabled because I also have macOS installed on the same computer.

Since I installed a Gainward GTX 1060 6GB Phoenix in the same slot previously used by the GTX 760, the monitor turns on but it's empty and I get the message of no signal available, until the login screen of Windows 10 appears. No booting screen is shown.

I tried both "normal BIOS" and "backup BIOS" (the physical switch) of the GTX 1060.

I tried to enter the UEFI and I think it works, because after an unusual time I was still waiting without W10 login screen, but I couldn't see anything.

I'm especially worried because probably I won't be able to see the "Windows updating" boot screen and that means that sometimes I will have to wait without any idea why and because I won't be able to access the UEFI in case of need. Also, no access to macOS.

Drivers and UEFI are updated. I have no way to know if the GTX 1060 BIOS is updated, since there are no updated available by Gainward.

I tried all the three Displayport connections.

How can I solve the problem and see the bootup process normally?

Edit

Following the suggestion from the comments, I tried again all the ports. With Displayport 1 I get the behaviour described.

With Displayport 2 or 3 the boot does not proceed, I guess, because everything is black and brief-pressing the power down button brings down the PC immediately, while it should take some seconds if the login screen were ready (albeit invisible).

With HDMI I can see again the boot process. This means that somehow HDMI is the first display.

The question stays: how can I see the boot again, with Displayport?

Answer 1

It appears that solving this issue is not possible without manufacturer help (unlikely, Gainward is a low-cost manufacturer from what I understand).

In this answer it appears that the graphic card could either duplicate the output on all ports until the drivers are loaded, or output only to "port 1", which in my case appears to be HDMI. My card does not have a setting to change the behaviour and it does not detect whether Port 1 actually has a monitor connected.

Which screen gets BIOS output during the boot process is up to the graphics card. Some graphics cards output to all displays simultaneously, some will only output to whichever port it considers to be "port 1". Most of the time they're not labeled. In the case of multiple graphics cards, the display goes to whichever one the BIOS detects first. Some BIOSes have a setting that lets you determine if an onboard vs. discrete card should be treated as the "primary".

...

Also... some BIOSes do not detect whether or not a screen is attached to the primary display and some do. In the cases where it does, "port 1" might change depending on whether the TV is on or set to the right input. In cases where it doesn't, output may go to the HDMI port whether there's anything connected to it or not, and you may not see anything on either screen.

Answer 2

Most (I haven't happened upon any that don't) graphics card have a specific port or port type (e.g. HDMI, DVI, DP) that is the "standard" one, in my case it has often been DVI. That means that on booting the system, only this port will show something. My suggestion is to try both HDMI and DVI and see if they don't work.