Dell S2716dg, computer does not detect (goes into safe mode immediately)

I need some help, I think the error is not from the monitor but from my computer.

-Connected by DP unto my GTX 970

-Windows 10

-I have my main monitor (ASUS vg248qe) still connected by Dvi in my GTX970

When I start my computer, my asus start normally. The dell goes into safe mode right away. In the Nvidia control panel, it only detects the asus.

I tried all 3 dp port, only one seems to work. (the other two doesn't even show the safe mode message)

I tried plugging the dp port the other way around.

I tried unplugging the power cord off and the on.

I tried unplugging my Asus completely.

I tried changing my power option to high performance.

I disabled the fast boot option in my BIOS.

I updated my graphic cards and the nvidia geforce experience.

I plugged the HDMI into a laptop, and switch the display to hdmi then it worked! I was able to disable the deep sleep mode, and did a factory reset.

But when I use the DP into the GTx970, it still goes into safe mode. My theory is that somehow, the computer does not detect the monitor and it goes to sleep right away.

Thank you all for your time, I am looking forward so much to try 1440 and G-Sync!