MW2 Not Workin...

Every time I put in my MW2 disc in my PS3,it takes me to the Infinity Ward logo and in the middle of the animation of it,the screen goes black,and it takes me right back to the XMB Menu....it first happened to me earlier this morning and I had to take my disc out and I found a mark on the back....I tried to get it off but accidentally left a fingerprint.I put the disc back in and had no problems.Now it's doing it again,but there's no mark,and I take the disc out and it still don't work.If I take the disc out either it still goes to the Infinity Ward logo and takes me back to the XMB,or it lets me get to the Multiplayer menu and I go on "Play Online" and after the popup "Connecting to the macthmaking server." comes up,it takes me back to the XMB.My MW3 though,works perfectly.Same with my LittleBigPlanet 2.Anyone know how to fix this?And I don't think I have any "torrent" thing on my computer....I play it on my PS3 and not my computer....also my friend isn't having any problems with his MW2.....any help???