(Sorry for my poor English)
Actually the problem lies on the Eject button. Those who had the PS4 lie down, the Rubber below the button might somehow hit it. Another reason is for those who had it horizontal or vertical, the button might be dirty, greasy or static charged (maybe).
I have this problem while my PS4 is vertically placed. I tried placing it horizontal, but failed. Initialised the PS4, still failed. Change power socket, failed. Then I came across a forum on the eject button. I tried to clean the button with a clean fibre cloth (top and front surface of the button) and try to pull the rubber beside the button off the button, it works!!
I had a similar problem several days ago I didn't come across this post until now. My problem was the opposite though. I was switching disks and suddenly it was continuously trying to eject and would not take in my disk. I ended up power cycling my PS4 and afterwords It worked. If I have another problem I will give more detail on what happened.