Hi, welcome to the forum!
Don't worry, there are many possible fixes for this.
One of these solutions should fix the problem.
I'll list some:
-Try a different browser.
-Reinstall Unity (Uninstall then restart your computer, install new version, then restart computer again.)
-Delete 'game files' which is an option on the website: http://fusionfall.cartoonnetwork.com/help/uninstall.php
Try an older version of the Unity web player.
-Try the newest version from the official Unity 3D website.
-Try the BETA version of the Unity web player from FusionFall. (Uninstall Unity web player, launch game
and then it asks you to download it, which will give you the BETA version.)
-Clear your browser caches and cookies.
-Try lowering your in game graphics settings to 'Best Performance'. (Maybe you should even make the
"Sometimes you gotta run before you can walk." - Tony Stark, Iron Man.