Can't watch movies online

Hi so I just recently bought a 13" Macbook Air. So of course I wanted to go to youtube to see some reviews or tips on my Macbook but youtube videos won't play. All I see is a black screen, no pause button, it's not buffering. I saw a post saying to turn off plug-ins in the preferences. And yes, it worked. But now I want to watch movies online, I can't because it's says I need to install Java. I don't get it? Shouldn't the turn off plug-ins do the trick? I'm new here so please help me. It will be much appreciated. Thank you