Refresh your browser:
Try this first!. Refreshing your browser often resolves video display issues.

Install the most recent version of Adobe Flash Player:
1. Uninstall the version of Flash you're currently running before upgrading. For instructions, click here.
2. Download the latest version of Adobe Flash Player by clicking here.
3. Exit your browser, then install the downloaded version.

If the instructions above don't resolve the issue, please also try the following:
1. Check your browser settings to ensure Javascript is enabled (turned on).
2. Temporarily disable popup blocking software installed on your computer.
3. Allow YouTube.com as a trusted site in your Firewall software.

For Windows Vista users:
If the Flash uninstall/reinstall doesn't work, this may be due to a Vista permissions issue.
Please use the Windows button at the bottom left then the search function:
1. Go to: C:\Windows\System32\Macromed\Flash\.
2. Right-click on the following file: FlashUtil9b.exe or FlashUtil9e.exe.
3. Select "Run as Administrator" and install the update..
4. Restart your computer.