Tennis racket strings broke from top after 5 minutes of playing?

I've been playing tennis for about 8 years now and I have never seen this happen before. It's the first time I've tried the Luxilon AU big banger and this is a new racket Head Prestige Pro. 5 minutes after playing I shanked a forehand and what do u know, the top strings snapped. Anybody know why this happened? I'm so pissed these strings cost $17 for 1 roll!!!