AHowes
Not sure it can be a bios issue when your friend has the same monitor and your card worked there on his.. maybe his monitor has a different firmware then yours or your monitor just won't save whatever info it senses off the gpu so it will work right with the hand shake.

We bought the monitors the same day, in the same cart. besides, the display works just fine on windows, its just that the uefi gop bios of the graphics card is unreadable by the motherboard... that's why there's no display before windows starts, I believe. Keep in mind, the 1080 did work fine on my system for a while, then the issue came back after a restart (nothing changed in the system).

Ok.. if the bios flash dont work I'd think about taking your monitor over your friends house with your cable and 1080 and slap the 1080 in his and try your monitor and see if he can get into the bios.

Maybe swap monitors with him since there the same hehe.


Anyways that's the weirdest issue I've read about.. hope ya get it figured out soon.

 When you were using your card in your friends system did you ever restart his machine to see if it would black screen on his system?

My friend's system had an nvidia gtx 770 installed before, we removed it and installed my 1080 in its place, we tried restarting (both from case button and windows), shutting down, cold boot(after turning off psu power) and it worked fine just like my system after installing another card then the 1080 back. mine could not read the UEFI GOP BIOS of the 1080, then we put in another card (evga 970SC/MSI 1060), boot the system, shut it down, put the 1080 back and it works just fine (for a while).
 
I suspect that the motherboard caches/reads the graphics card firmware/information and it expires after a certain period of time then the issue comes back.. the MSI 1060 and the evga 970SC worked just fine from first try, even when the issue existed, when installing the evga 970SC or MSI 1060, the motherboard reads their UEFI GOP BIOS just fine, then I put mine back in without changing anything and it works just fine (again, for a while), then the issue comes back randomly when my system is posting, and stays until I boot the system with another graphics card.
 
 
Update: look at http://forums.evga.com/1080-FTW-non-CSM-boot-m2559407.aspx
There are two other people who have the same symptoms as me on their 1080 FTW, couldn't see boot sequence, no display until Windows loads with CSM disabled. 

I don't understand the point.. are you saying this is some flaky 1080 ftw issue??

You did say your card worked perfectly in his system and monitor without your issues.

So in the end that tells me it must be something in your motherboard.

Old left over settings conflicting it from working correctly.

Pull the Motherboards cmos battery! Remove it and drain the caps by also unplugging the psu 24 pin connector and the 4/8 pin connector and hit the power button a few times on the case and still wait like 10 mins to be sure.

Put the battery back in as one would think now it would wipe any past saved settings and try again.

AHowes
I don't understand the point.. are you saying this is some flaky 1080 ftw issue??

You did say your card worked perfectly in his system and monitor without your issues.

So in the end that tells me it must be something in your motherboard.

Old left over settings conflicting it from working correctly.

Pull the Motherboards cmos battery! Remove it and drain the caps by also unplugging the psu 24 pin connector and the 4/8 pin connector and hit the power button a few times on the case and still wait like 10 mins to be sure.

Put the battery back in as one would think now it would wipe any past saved settings and try again.

It worked in his system because he had another card installed before (770), for me if i install another card then the 1080 the issue is gone for me too (for a few hours).
I did remove the cmos battery, turn off the PSU, turn on the pc to reset the pc and clear the bios settings, i even had it unplugged for 1-2 hours, all the bios settings did reset.
 
This might be relevant:- that person has an evga 1080 FE, he had a 970 with no issues, isntalled 1080 black screen, reseted bios with 1080 issue did not go, installed 970 and reseted bios then put the 1080 back and his issue is gone.
https://forums.geforce.com/default/topic/957634/geforce-1000-series/brand-new-1080-founders-edition-and-no-signal-fixed-/1/
 

Looked like his black screen fix was to reset the mb bios (pulled cmos batttery) and load optimised default settings and reinstall the 1080.

Still could be an issue with another setting on the board like do you have the main gfx set to pcie or built in as in the gpu built into the cpu?

I believe there's a setting to turn off the built in gpu. I think there was on my z97 board but don't see the option on my z170 but just an option to choose the main display on built in or pcie.

AHowes
Looked like his black screen fix was to reset the mb bios (pulled cmos batttery) and load optimised default settings and reinstall the 1080.

Still could be an issue with another setting on the board like do you have the main gfx set to pcie or built in as in the gpu built into the cpu?

I believe there's a setting to turn off the built in gpu. I think there was on my z97 board but don't see the option on my z170 but just an option to choose the main display on built in or pcie.

Already tried turning the igpu off without success. /that person said he reseted the bios but it didn't work, the issue did not go, then he plugged in a 970 and he saw the boot sequence, then when he put the 1080 back the issue went away.

Well when I had my many 1080s "12" (as I was exchanging them left and right trying to settle with a set for sli to settle with) I only remember encountering a simular issue early on. I first got 2 zotac 1080 amp cards. When testing them 1 by 1 I encountered the black screen issue where it wouldn't turn on the screen, just stay black.

I was using the display port and there were like 3 ports and I would swap ports and it would finally come on. It wouldn't happen everytime. Sometimes I had to unplug the cord from the card and reinsert it over and over and wait for the display to turn on.

Was thinking it may be a bad port on the card though later on just figured it was some kind of hand shake issue.

This also happend with the next set of 1080s. The pny fe 1080. With it happening on different cards I figured yeah it was some hand shake issue with the card to the monitor. Sometimes I'd even turn the power on and off on the monitor to get it to work. Was annoying.. then I exchanging them for evga fe cards cause I wanted to put water blocks on them and evga was cool with that and on pny it would void the warranty.

Same thing would happen with them with the once in awhile black screen trying to turn the system on. Sometimes I even gave up and turned the power off on the pc and powered on to get it working.

Anyways I finally upgraded the bios on the motherboard "asus maximus hero vII z97 and for the first time I seen a 1080 bios post screen I never noticed prior. Was strange.

Figured it was just some fast boot setting I was using prior on the older bios that I was not using this time on the newer bios.

Anyways never experienced an issue after that bios upgrade so maybe it fixed it or it was not using fast boot.

On the new motherboard asus maximus hero VIII alpha Z170 I never see the 1080 post screen either though I don't see a fast boot option either.. could be there? Anyways all I see is the asus post screen graphics and then the windows log in screen.

The z170 is known for booting slower then the z97 even though I'm now also using a faster samsung 950 pro m.2 drive.

EZtouch

AHowes
Looked like his black screen fix was to reset the mb bios (pulled cmos batttery) and load optimised default settings and reinstall the 1080.

Still could be an issue with another setting on the board like do you have the main gfx set to pcie or built in as in the gpu built into the cpu?

I believe there's a setting to turn off the built in gpu. I think there was on my z97 board but don't see the option on my z170 but just an option to choose the main display on built in or pcie.

Already tried turning the igpu off without success. /that person said he reseted the bios but it didn't work, the issue did not go, then he plugged in a 970 and he saw the boot sequence, then when he put the 1080 back the issue went away.

What I took from it is that he feels the clearing of the cmos and slapping the 970 back in and getting into Windows and uninstslling the prior gpu drivers using DDU and then installing the 1080 and seeing it post for the first time he felt that fixed it.. though we all know uninstallling the drivers first didn't fix it but it's obviously the right move to uninstall the old drivers first anyways when replacing a card so it won't interfer with the new card.

So you feel since he put the 970 back in the mb and held the cards bios so when he put the new 1080 in it worked cause it was still holding the info from the old card and eventually won't work soon after again't cause it will loose the old info.

I'm not sure that's how it all works. Would think the only info being passed is from the card to the monitor but yeah the motherboard would be allowing the card to send it.