Internet Connections

Hello,
I recently had to reformat my computer because it wasn't working. After my dad reformated it, he installed the basic things I had on my computer before; Windows Live Messenger, Limewire,Norton,Java,Adobe Reader etc. Whenever I go on the internet I usually go to youtube or bebo, when I try and login to my acounts it just says "Cannot Display Webpage". Before I reformated my computer I could login to all of my favorite sites and it wouldn't say anything about the connection and when im on my laptop I don't have any problems either. I don't know why this is happening and it's really getting on my nerves. It happens all the time and after it says it cannot display it I check my internet connection and it says it's working 100% fine and I try again and still nothing has changed. Please if someone knows how to fix this problem tell me a.s.a.p, I have tried alot of different things and usually I am pretty good with technology but this time I need help so please if you know how to fix this problem tell me.