As has been indicated, Flash is due to disappear at the end of the year, as it presents too much of a security risk. All major streaming websites (including Youtube and the BBC) abandoned Flash, and switched to using HTML5, several years ago.
Start by trying a different web browser. If that fixes the problem, return to your default browser and use its 'reset' procedure to return it to it's 'fresh out of the box' state. (If you need instructions, please tell us which browser you use).
If the problem doesn't disappear when you use a different browser, you might need to reinstall the video drivers. (Again, instructions upon request).