I came across a DisplayPort cable & Nvidia setting issue with my new EVGA GeForce GTX 1070 graphics card connected to dual BenQ XL2430T monitors that I spent a good half day troubleshooting before finally resolving that I would like to share in the hopes you don't run into this same issue.
When I initially purchased the EVGA SC GeForce GTX 1070 and installed it into my dinosaur of a PC (Asus P6T Deluxe MB (, 16GB RAM, 1TB SSD), I didn't realize that the 1070 card didn't come with dual DVI-D ports as my older EVGA GeForce GTX 680 had until I installed the card and went to connect my DVI cables to my dual BenQ XL2430T monitors. The GTX 1070 has 1 x DVI-D, 3 x DisplayPort interfaces, & 1 HDMI interface. I hadn't even heard or knew anything about DisplayPort nor did I have DisplayPort cables so I ended up connecting the only DVI-D port to 1 of the 2 monitors and connected a HDMI cable to the other monitor. Problem solved.
Some days later, I started reading up on the DisplayPort (DP) interface curious as to why EVGA seemed to be so gun-ho about having so many DP interfaces on one of their high end graphic cards and clearly the advantage of DP over the other interfaces -including HDMI 2.x is its bandwidth capacity and support for 4K Ultra HD. So I decided that, while I don't have a pressing need to play games at 4K, I would like to have a matching cable set from the GPU to the monitors and using DP is the only way to achieve this. I went out to Fry's Electronics in CA and purchased a couple of good quality 10ft DP cables, got home, removed the DVI-D and HDMI cables, and plugged in the 2 x DP cables and was back up and running with my new GPU in no time.
Once I had the DP cables installed, I started playing with the Nvdia Control Panel settings and through some careless combination of my choices I ended up locking out the display of 1 of the 2 monitors. What I mean by locked out is the monitor still had power (the power button was still glowing white) but the display was black and the monitor's menu buttons on the monitor and the BenQ's external menu paddle where unresponsive to inputs unless I disconnected the DP cable first. And because the desktop was stretched across both displays, I could only see and work from 1 of them. Now if I disconnected the DP cable from the locked monitor, the monitors power button would turn orange, Windows 10 would auto adjust the desktop to 1 monitor and I could continue working. If I plugged the DP cable back into the locked monitor, it would revert back to the same display issue.
I thought maybe I somehow corrupted the Nvidia drivers through my carelessness so I completely removed all the Nvidia drivers. To make sure I removed all traces of Nvidia drivers I not only ran the typical uninstall from Control Panel > Programs > Uninstall but I also downloaded, installed, & ran the Guru3D.com DDU (Display Driver Utility), then rebooted my PC.
Once I logged back in I downloaded and reinstalled the latest Nvidia drivers from the EVGA support page (v378.78). I then re-attached the DP cable and still no change! I swapped DP cables with the known good one -no change! I swapped DP ports on the GeForce GTX 1070 -no change! By now I was running out of options. Both cables worked initially so despite a lot of Google hits concerning bad DP cables out there I really felt it a stretch that suddenly the cable would stop working without some kind of physical damage in between and that didn't happen. So I went back to where this all started -the Nvidia Control Panel Utility (NCPU) and on the only working monitor proceeded to click through all of the features and options to make sure they got reset to factory default (although presumably a complete uninstall and reinstall of the NCPU should have done the trick).
Going down the menu options on the left of the NCPU I started going to each section then select and apply the "Restore Defaults" link in the top upper right. When I got to and expanded the display options, I clicked and highlighted "Change Resolution". The right-hand pane displayed the 2 connected monitors (despite 1 of the 2 not displaying anything and power button on), how each monitor was connected (both said DP), and a choice of resolutions below the connector icon. The resolution choices are broken up into 2 x sections. The first section is for Ultra HD, HD, & SD with a long list of available resolutions and the second section is for PC and underneath it another long list of resolution options.
When I clicked on the graphic of the monitor representing the one that I was working from, its resolution was set to 1080p, 1920 x 1080 (native) under the first section (Ultra HD, HD, & SD) but when I clicked on and selected the graphic of my second monitor, its resolution was set to 1920 x 1080 but it was set under the PC section. This difference got me to thinking and when I scrolled back up and under the Ultra HD, HD, & SD section selected the same resolution as my working monitor: 1080p, 1920 x 1080 (native), then clicked apply -WAHLAH! The monitor display kicked on and Windows 10 readjusted my desktop across both monitors correctly. Case closed! Lesson learned!
Save yourself a lot of frustration and time and research what an applications features and options do before carelessly poking around and making changes. As long as I have had a career in IT and played with computers as a hobby I should have known better and now hopefully you will too.