Why is my computer crashing this way?

Ok, so Im playing World of Warcraft, and me and my arena team are in the heat of battle. The match is getting close as a teamate falls right after an opponent is slain. As the number of dead gladiators rises it apears that it has finally narowed down to me and 1 opponent. We lock gazes as I push out the cheering and quick battle tips from my dead companions rooting me on. As the excitement builds up between me and the other fighter, we meet head to head in the midst of the arena and ferociously clash and parry our swords. Before the other gladiator relizes it he has made a terrible mistake in his battle rotation, leaving him vulnerable to attack. He knows he has been bested even before I deal the final blow. I raise my sword, preparing to thrust it through his skull then all of a sudden- SCREEEEEEEEEEEECH -_- My heart jumps as a solid color screen apears on my monitor with a loud background noise of what seems to be pacman on steriods. I cant even describe to you in words how frustrated I feel at this moment. Ive let down 4 of my teamates all because of what? A technical difficulty? Its just ridiculous. What could be causing this? It happens very frequently and it is very anoying. The solid colour is random every time and the noise is just god awful. The only way to fix the problem is to manually turn off my computer with the power button. I use Windows 7 and I have a dell labtop. Why is my computer crashing this way?