Make sure you are using the latest version of Flash for each browser. See the Flash version checker webpage in each browser, and check if you are using the latest version for that browser. If not, update your copy of Flash for that browser: http://get.adobe.com/flashplayer.
Verify if the latest version of Flash is installed properly per browser. In Firefox and Chrome, type
about:plugins. For IE, go to the Tools Button (gear icon) - Manage Add-ons (detailed instructions here). This should list all installed plug-ins and their versions. You can also recheck at the Flash version checker webpage.
IE uses different Flash plugins (and has a different installer) than Firefox and Opera (there's an IE version and a non-IE version of the Flash installer).
The Google Chrome browser (32-bit) includes Adobe Flash Player built-in. Chrome automatically updates when new versions of Flash Player are available... Select About Google Chrome under the Tools menu to verify that your Chrome browser is up-to-date. (The wrench icon near the Chrome address bar indicates the Tools menu.) It can take some time before updates roll out to all Chrome users. (Source).
Opera has a 64-bit version, and that version can use the 64-bit Flash plugin. Also, starting from Flash Player v11.3, the 32-bit and 64-bit installers for the same browser types are the same. This means that if you have a 64-bit version of Windows, the Flash 'universal installer' will install both the 32-bit and 64-bit versions of Flash for that installer's browser type.