NEED HELP WITH MY Inspiron 1545???

I recently purchesed a Inspiron 1545 from Buddys Homefurnishing the lap top is brannew, never been used.  I get home and fire it up and it runs great, I run a virus check dose good no viruses deteced then I want to see all the cool things that are available pop in a movie to see sound and picture quality, move never come on never plays.  Then I try installing World of War Craft on my laptop it gets half way threw italaton and the computer freezes nothing works even the mouse is frozen. I try to get on the enternet and it works for a few minuts then it feezes again any aplication I run it freezes, what is going on Please help