Videos will not play, images are sometimes distorted, blue screen when I open my laptop?

I have a 2011 13" MacBook Pro, and lately it has been having a lot of issues. Videos come up as a black screen, and many images are distorted, such as around the tool bar and my screen saver. Every time I open it this pale blue screen comes up, then vanishes after a few seconds. It hasn't done this in a while, but it also started making this strange stuttering sound sometimes when I played anything with audio in it sometime this summer. I have been having the same problem for the past month or so. I have gone in to get it looked at twice. The first time they found some sort of software problem, which they fixed. The second time I went in they ran some diagnostics and made sure it wasn't the graphics card. The only thing they did was replace the battery. After both visits the computer worked perfectly for about a week before coming down with the exact same problems. These were at two seperate stores. I still have a few more months left on my warranty, but I am getting frustrated. Does anyone have any idea what the problem could be?