what do different quadrants mean when they’re lit up on a 360 with the red lights of death?

sometimes its the upper left one lit up (from a horizontal position) with the upper right blank and others its the upper right one lit up with the left unlit but the bottom two are always lit up. Christmas is a few days away and I wanna be able to play Assassins Creed and Call of Duty 4! PLEASE HELP!!