By the look of it some kind of server or tower workstation (actually analogue). And you can find the specification on the system unit where it will be the description of this button. Actually, if I remember correctly it should be the signaling for the BIOS that the cover is open and it is necessary to run the cooling full. I don't know you have the regular cooling system or not, but the staff can not work when the lid is opened when violated, we calculated the path of the air flow, then it won't cope under load. Therefore, the system unit and yells as the victim when the lid is opened. The idea of these system units is only opened to replace hard drives or power supplies hot-swap. So understand why when the lid is closed the button is not pressed, it is possible there is a broken focus.