Not sure about PS4, but on xbox you have to make sure you have the HDMI plugged into "HDMI OUT" on the xbox, not the "IN" slot. So if there is something similar on the PS4, try switching the HDMI to the out port. Then try pressing the button on your monitor again to switch to HDMI. This usually works for me.
im pressing the menu button under the monitor to open the menu then pressing the input button to switch. it automatically should switch but it most of the time it doesn't.
it might be my computer settings but i dunno where to look
Not sure about PS4, but on xbox you have to make sure you have the HDMI plugged into "HDMI OUT" on the xbox, not the "IN" slot. So if there is something similar on the PS4, try switching the HDMI to the out port. Then try pressing the button on your monitor again to switch to HDMI. This usually works for me.