Just going to Run something by you, if I remember correctly WOW Vanilla on a Multi Monitor setup always picks Monitor “0” When on an Nvidia card. Monitor zero will always be the DVI port if you have something plugged into there. Which I see from your DXdiag is plugged in. If you are running the displays so that the one plugged into HDMI is primary and the one on DVI is secondary in windows, you could have a potential issue.
I owned this card for a bit, I distinctly remember being frustrated that I couldn’t 3d game on one of the ports due to the cards hardware limitations. I had to switch my displays around so that 3d rendering happened on the “Main display” (set in windows or Nvidia control panel) since that version of wow wanted to be on a specific port on the GPU. That caused the client not to start. In the End I didn’t want to run 3d games on that monitor (My new monitor was/is DP and HDMI only) so I chucked the second display and went single.
Try unplugging the Monitor on the DVI port if it’s not your main, or just try one monitor. I used to own that card and a 960, I remember having a limitation which monitor was actually set to main in windows for gaming. Two issues I remember the most were it stayed in full power state when running multiple monitors (So it would never clock back down), and it would only game on the monitor that is “0” (Zero) on the physical card. if something is in the DVI port that is always zero. If whatever display is connected to the DVI port IS NOT, display ZERO or “Main display” in windows, wow would not start.
Again I am just vaguely remembering this, years ago, lol. I think this is how my beautiful samsung monitor ended up in my garage plugged into my file server. I think the only way to get wow not to throw an error while starting was to go out and buy to displayport to HDMI cables and back then they were like $50 to $75 a pop, I was like nah, I can just have my laptop on the side. lol.
TL;DR wow (that version) wants to run on a specific monitor.
SIde note, if you are running Discord, try disabling in game overlay. That could be the issue with some pre “GPU accelerated hardware scheduling” Cards. WHich your card falls under. (Maxwell series cards) Geforce also has an overlay that is on by default. Steam too.
Here is another forum post with the same issue.
The archives don’t go back far enough for when in posted unfortunately. I remember posting a solution too.
Good Luck.