S2716DG, DP suddenly not working?

Hello,
System details:
windows 10 64 bit,
motherboard: ASUS H170M-PLUS
GPU: ASUS STRIX-GTX970-DC2OC-4GD5
CPU: i7-6700K 4GHz

the monitor have been working fine for a while - till I downloaded a game called (Rainbow six siege) the screen went dark then switched to sleeping mode -- I restarted the PC - and now I can't even get to windows- I can see the Asus logo and can access the bios - but when it's on the windows boot screen (the picture before getting into windows) it goes to power sleeping mode (via DP cable).I switched to and HDMI cable and it works fine.

I Updated the Bios/Updated GPU Driver/Installed the monitor driver/did the hard reset/+ tried a suggested solution elsewhere to boot with hdmi cable and then disconnecting everything for 1 minute(I waited more) and then plug in the DP cable while the PC + monitor where on, But nothing works
I read the forums with same problem but nothing worked for me.

I don't know if this helps but The game has and option to run with VULKAN API (over directx11) --which and I quote: "enable us to make improvements on workload through Dynamic Texture Indexing to reduce CPU cost, and Dynamic Resolution and AsyncCompute to reduce GPU cost. These features are already used on consoles, and the Vulkan API will allow us to do the same for PC. By combining all these features, we can optimize both the GPU and CPU cost of rendering."
I played other games and they where fine and also played previous versions of this game with Vulkan and it worked (same monitor).
The monitor was problematic since I bought it on 04/2020 - colors were faded with a yellow tint + had sleeping mode problem before -I managed to fix them through the forums on the internet--(disabling Deep sleep+updating drivers+disabling sleep mode for the monitor from he control panel).