If you're on a console, hold down the button to open your pip boy (inventory) instead of just tapping it and the light should come on, if you're on pc, read your instruction book because I have no idea.
ZOMG is just another variant of OMG. Probably started out as a typo or somebody just randomly decided it would be cool...who knows with these sort of things.
He who fights with monsters should be careful lest he thereby become a monster. And if thou gaze long into an abyss, the abyss will also gaze into thee. - Friedrich Nietzsche