There are a few possible reasons for this issue.

1. If your Internet connection isn't fast enough, the video may be getting stuck while it downloads. If that's the case, you probably need a faster connection. For example, dialup isn’t fast enough. And if you're sharing a connection with lots of other people -- or even a couple others who are using a lot of bandwidth -- that can slow down your video too.

2. If your computer doesn’t meet the minimum technical requirements listed here, you may want to upgrade. Please check your hardware against that list, and make sure your browser and Flash player are up to date. You'll find the latest version of Flash here: http://get.adobe.com/flashplayer/