In order to activate the power, you need to press on 5 buttons across the map, they are pretty obvious since an icon shows you where they are when you enter an area.

The Pack-A-Punch is located in spawn, but gas is preventing you from accessing it. In order to drain the gas, you'll need to rotate 5 statues around the map. When you restore power, icons will show you where the statues are when you get close to them.

Pack-A-Punch will then be open for one or two round, after that you'll need to rotate one or two statues again to make it accessible, be careful, if you get in the area between round, you can die from the gas.