P2715Q, DP, Cannot see Bios or Boot screens

Hello,

When I purchased this monitor several months ago, I had many problems when the monitor turned off and PC was on. The native resolution is 4K and Windows was changing applications positions/messy resolutions and I followed these steps:

en.community.dell.com/.../19580375

Those steps worked for my case (not the same monitor in the original's post). But I haven't been able to see pre-Windows boot screen information ever with DP cable.  If I want to check something in BIOS setup or try accessing safe mode for example the screen is completely black. What I have to do is plug in an HDMI cable and switch to HDMI mode in my monitor in order to see bios/startup information. I bet there is something messed up with the DisplayPort configuration in the registry editor? I don't like using HDMI cable because the frequency is lower than DP so I just use it when I want to see something at startup but its kind of annoying. There is a legend/popup on monitor when I recently turn it on: "Entering power safe mode".