If you're running into difficulties displaying Flash video, one of the first troubleshooting steps is to disable hardware acceleration in Flash Player. If you are using Internet Explorer 9 or higher, please see the bottom of this page for instructions specific for your browser.
It's a simple process but I've seen situations where getting access to the "Settings" dialog has been disabled. Because of that, I'd recommend the following:
1. Navigate to the Flash Player Help page.
2. Scroll down to the "tree" animation
3. Right click on the animation and select "Settings"
4. The Settings dialog will appear, change the tab at the bottom to the display (if not already there) and uncheck (or if you'd like to enable, check) the "Enable hardware acceleration" checkbox.
5. Close the dialog and restart your browser.
For Internet Explorer 9, 10 or 11 users, please follow the instructions on the following page to enable software rendering: https://support.microsoft.com/en-us/kb/2528233