How do I fix my laptop?

I bought a new gateway laptop two days ago and I am already having trouble with it. For some reason it won't load anything past a certain point. No matter what it is it will only load about a quarter of what I want. itunes wont load all the way and youtube videos won't even play. I already set the settings to unlimited for how much it can hold but it hasnt made a difference. I tried contacting gateway and they keep telling me that my serial number is incorrect. I have tried allthe numbers on my laptop and am positive I have entered the right number. I dont know wnat to do, they wont help me. Please help. thanks so much.