I had a similar problem when I first hooked my PC into my 144hz monitor. I used the dp cable that came with the monitor but it wouldn't support the faster refresh rate. I bought a new cable and boom! It worked.
If cable is problem make sure to buy do 1.4 or hdmi 2.0b
Also...you have actually gone to the advanced display adapter settings in windows and tried to set your monitor to 240hz right?
I had a similar problem when I first hooked my PC into my 144hz monitor. I used the dp cable that came with the monitor but it wouldn't support the faster refresh rate. I bought a new cable and boom! It worked.
If cable is problem make sure to buy do 1.4 or hdmi 2.0b
Also...you have actually gone to the advanced display adapter settings in windows and tried to set your monitor to 240hz right?
in your sceen-shot I saw ram speed as 2133. With a 3700x you will get some performance-enhancement , if you enable DOCP in BIOS and choose the higher ram-speed ( does not have anything to do with your refresh-rate-problem).