Internet problem with Multiplayer

With 1.6.2, whenever I click the Multiplayer tab, it shuts my internet off. It works just fine for 1.5.2. So I log on, do all of that and it works just fine, as does Singleplayer, but when I click on Multiplayer it turns my internet off. I've tried fixing it by reinstalling Minecraft, but that didn't work. I also tried disabling my firewall and using it but that didn't work either. Any help is appreciated, thanks.