1080p videos will take longer to load. If you are watching it while it is still loading and the "where you are" dot hits the end of the red "how much is loaded" bar then the video will freeze. Could this be your problem? I mention this because you said it freezes not something like it becomes choppy.
I agree that it sounds like the video just hasn't come in yet. You can pause the video until it's loaded enough so that you can play without stopping.

If that's not the issue then be as clear as possible about what is wrong.

Also, if that's no the problem then you can try using a different browser. Firefox, IE8 and Google Chrome are the top three.

Make sure you have the latest video driver for your graphics card.