Why cant i sign into any of my accounts on my computer?

Last night i was on my computer and while on facebook, the page just shut down and said that the webpage is not available. I refreshed the page a few times and it still wouldn't work. I tried going onto twitter and it didn't work either and the same thing was coming up. So i went on to YouTube and wanted to watch a video that had mature content, it was an itskingsleybitch video for any of you who thought it was or something bad or whatever. So i tried logging in and it wouldn't work. I tried logging into my aim, it wouldn't work. I tried logging into my oovoo, it wouldn't work. Nothing is working and i cannot sign into ANY accounts. The only thing i can go on is my email yahoo and tumblr and that is because i was signed out of it. Why is this happening and how can i fix it?