You're reference is to Flash Player, and apparently Internet Explorer because you specifically say "manage add-ons" which is a term associated with IE
Not sure what all has happened, but you might go here to try to re-install.
If it gives you the option for an additional feature like Chrome or a toolbar, or an antivirus feature uncheck that!
It should autodetect your OS and Browser.
BEFORE you try to reinstall you might want to run an uninstaller just to clear out whatever Flash is there. You can find that here.
Alternatively you might try Firefox (which requires a separate Flash install). I have pretty much stopped using Internet Explorer. Though ironically as I somewhat bash IE, flash does have a tendency to crash in Firefox now and then. Luckily it operates as a separate process though so it doesn't crash the browser session.