Here are some hints on troubleshooting QuickTime problems.
1. You can check your QuickTime installation at the Apple QuickTime Installation Check site at http://www.apple.com/quicktime/download/
2. The Apple web site has a Live Streaming Check to check for problems (e.g. firewall problems), see http://www.apple.com/quicktime/troubleshooting/streamingcheck.html
3. Perhaps you are having trouble just with our videos? You can try viewing other videos, for example, try viewing one of the movie trailers from the Apple web site at http://www.apple.com/trailers/
4. Still having trouble? You can see the QuickTime Support page at http://www.info.apple.com/usen/quicktime/ .