Windows 7: Unable to connect to server browser problem.

Hi,
I'm sorry if I've made/posted this in the wrong place; I'm new here and I've come across a problem with my browsers. It started around Tuesday of this week, where I've logged into a website such as Tumblr and the type boxes/sections come up with a "Unable to access" etc on all the browsers; this has also happened with other websites such as Photobucket and chatbox functions.

I've looked through my settings, such as clearing caches and proxy, but that doesn't seem to be the problem. My computer runs on Windows 7. I have a feeling it might be the firewall, but I want to make sure of this first. I also have Norton internet security 2013 installed, however I'm not too sure of this because I don't want to re-install and then install it again, if that's not the problem.

So if there's any solution to this, could I have some directions on how to solve this problem. Thank you. C: [// also, I had to use my sibling's computer, which means it's defiantly not a home network problem; and it's just mine! ]