Okay ready?

So you go into a room. There are two computers and two doors. Door A and door B. One is the entrance to eternal happiness, the other leads to certain doom. Your job is to figure out which is which. You are allowed to ask one computer one question and one question only. One computer always tells the truth the other always lies. What would you ask?

i saw "labyrinth" and "the princess bride" so i dont feel i can answer this without cheating :)

Haha! I saw them and I still couldnt answer it. Attentiveness isnt one of my strong points, lol.