anybody gotten good at this?  help me.

in level 3 ive come to a dead end.  went back twice, everyone in the facility is dead, i have all the keys and as near as i can tell, ive been in all the secret rooms.  but then i get a dew rooms past the green door and it looks like a setting for a boss battle, but nothing happens, i just run and shoot at the walls like a tool until i get sad and go save and come here to seek guidance. 

somebody help a brotha out