Ensure you have the most up-to-date version of Adobe Flash Player installed, then clear your browser's cache and cookies, restart, and try again. If that does not work, please clear Adobe Flash Player's cache by following the below steps:
Go to http://www.macromedia.com/support/documentation/en/flashplayer/help/settings_manager07.html
Under Website Storage Settings at the top of the page, scroll through the list of Visited Websites until you find cdn1.static.tube8.phncdn.com
Select cdn1.static.tube8.phncdn.com from the list and click the Delete Website button.
Restart your web browser, open Tube8, and videos should play as normal.
If you are unable to follow the steps above, please search Google for instructions on how to clear Flash Player's cache for your specific browser.
If you continue to experience difficulties after performing the above steps, uninstall and reinstall Adobe Flash Player entirely. If you are unsure as to how to do this, please search Google or Adobe for instructions.