LCD Monitor Goes Black during Use (by 2 users)

I had the problem sometimes, but then I connected a second computer to the analog input and found out, that the screen didnt turn black but switches between the inputs on an on.

I found out that the "input" button seems to be short or damaged, as the behaviour was invertable by pressing the button. I blew into the button some times (a very naive solution, yeah) but it worked, the switching stoppped.