Help! No signal on displayport after Windows logo

[GuybrushT2]

I have a 980 Ti GPU in my HTPC hooked to a Panasonic AX800 4K TV via Displayport AND HDMI. The displayport is at 60Hz refresh rate for games and the HDMI is at 24Hz for watching movies and streaming Netflix, etc. I switch the input based on what I'm doing. Everything worked fine for months until recently. Now the displayport won't display. When rebooting, it displays the BIOS startup screen up until Windows starts to load. After the Windows logo comes on, the TV goes blank and displays No Signal. I can switch over to HDMI and it displays fine. I've tried everything including driver updates and switching the displayport on the GPU, but nothing is fixing it. There are a million similar posts on various forums, but I have not found a solution after exhaustive research. As a separate problem, I can't play games on the HDMI by setting it to 60Hz, because the screen keeps flashing black in the middle of a game. In an FPS, it only happens when I get shot and repeatedly at the start and end of a match. I don't get it. Anyway, I prefer to just get Displayport working again.

 

[GuybrushT2]

As an update, I was able to get the DisplayPort to work by unplugging HDMI from the TV. Obviously, it's not a great long-term solution to plug and unplug cables to my TV every time I want to use it, but I'm hoping that helps diagnose it. TV is not like a monitor, in device manager and such the PC doesn't detect 2 monitors by having 2 cables plugged in. The proper input on the TV has to be selected for the GPU to even register the connection, so I don't know why it would care that HDMI is unplugged.

 

[GuybrushT2]

That's the odd thing. I played a game on displayport, switched to HDMI to watch a movie, then tried to switch back to displayport for a game and it didn't work. No amount of restarting worked. I've had this setup for months and the problem just appeared and stayed. If I plug the HDMI cable in, displayport is immediately disabled and nothing will get a signal from it. If I remove the HDMI cable, displayport works fine.

 

[GuybrushT2]

The mystery deepens. I changed the HDCP setting on my TV from 1.4 to 2.2 (TV supports 2.2 but my 980 Ti does not - that's a whole other source of frustration). Setting HDCP to 2.2 effectively disables it because the GPU doesn't support it. Doing this allows both displayport and HDMI to work. Now that means that PowerDVD won't work without HDCP. But why would an HDCP handshake disable other inputs?