A:AnswerThe button is not on the face of the power membrane, but is slightly beneath and back toward the back of the schreen.
Put your finger on the edge and work back you will feel it.
My older AOC has it on the membrane.
A:AnswerThere are no mounting holes on the back of the monitor. I don't see how you could mount it on the wall unless you had a customized bracket that would go where the stand goes.
A:AnswerHave you tried changing the source on the monitor to make sure it is trying to read the HDMI input? I have had to do this on other monitors I purchased.
A:AnswerThe monitor does produce sound and shows up as a sound device under your sound options. While it does not have speakers, you can select the monitor as your source and plug in headphones/earbuds or speakers if you're doing a presentation on a desktop or if your computer headphone jack is otherwise occupied. It is just a nice, additional feature.