I got 3 red ring of death for no reason. WTF?

I was playing my xbox 360 for a lil while. Got off and went to bed. Then today when I got home, I try to get on and It went to 3 ring of death. It was weird. Cause I turn it off, never trying to play again today and It just went to 3 red lights. I went to gamestop to see if it was the power brink problem, and it did the same thing. It doesnt make any since to me. So any one had the same problem. Xbox is fixing for free but I just wondering why It did that. Thanks for all the answers :D