Sony Vaio internet connection problems?

I am running a Sony Vaio laptop with Windows 7, and for some reason, I'm having internet connectivity issues. It says I'm connected to the internet, and I can browse the internet in my browser, but other programs are having trouble connecting. For instance, iTunes can't connect to the store; Skype will sign in, but when I try to add a contact, it says I'm not connected to the internet; Vaio update can't connect to check for updates; etc. I've tried turning off all firewalls/virus scanners to see if that helps, but it doesn't, and I never had this problem before. It was fine when I was at uni, and I was connecting wirelessly. Now I'm home and using an ethernet cable, and I think that might have something to do with it. Any help/suggestions would be greatly appreciated. Thanks!