Why can't my desktop connect to most sites, but my laptop works perfectly?

My laptop can go anywhere, but my desktop can't go to MegaUpload(R), YouTube(R), Cnet(R), SourceForge(R), Rapidshare(R), etc. I can't even log on to any of my email sites. In fact, the only reason I can post this question is because of my laptop. I can't sign in anywhere, and I would like to use torrents for freeware, except I can't get anywhere with them. The ETA is always 8(sideways). Please help me. I share a computer with my little brother and he can't even play BOTS(R) or Fiesta(R).