Flash Player is well-known for ceasing to work properly, or for producing messages telling you than you need to update (even when you've already got the latest version installed).
Go to 'Add or Remove Programs' or 'Programs and Features' (depending upon which version of Windows you're using). Locate and remove 'Adobe Flash Player Plug-in'. Restart your computer. Go here to reinstall it:
http://get.adobe.com/flashplayer/
Chris