Question about Philips S-line 275S1AE

Hello I put the monitor into operation yesterday and everything works fine except for the following: I cannot operate any of the monitor buttons except the on/off button. If I try to adjust the brightness, for example, the monitor reports "Monitor controls locked". I found various blogs on the Internet where most people were able to solve this problem by pressing the Menu / OK button for about 15 seconds. Unfortunately this did not work for me, I pressed each button several times for at least 10 - 30 seconds. Even a power cap and restart did not help. I tried with and without the picture source connected - also on several notebooks. Unfortunately, this message still comes up. Can anyone help me? Thanks a lot