Halo 3 Easter Egg - Last Resort Computer

In the multiplayer level, Last Resort, head to the large building adjacent to the fan. Once in the center room, use either of the stairs on the sides to get to the platform overlooking this room, that has the switch to open the gate so vehicles may access this room. Hit the switch, and then you will see a parody of the windows, "Blue screen of death."
Go ahead and read what it says!

I forgot to mention, that It does NOT always Have this. Sometimes it will just say "system failure" in yellow letters. You can also do this on High Ground on Single flag games where you can open the gate.