More info will help people to help you with your problem.
What version of Flash Player are you trying to use?
What Operating System and browser are you using?
for example: Windows 7 or Linux, or a tablet or phone
Internet Explorer 10, or Fire Fox 22.0?
Have you uninstalled your old version of Flash Player after installing the newer one, and did you use the official Adobe (Flash Player) Uninstaller because using non-Adobe Flash Uninstallers is not always a good idea.
Also, did you check your installation, find what version is installed on your device, and ensure that the Flash Player was working properly (and follow any advice for troubleshooting) on the Adobe Find Version page? That page is here:
i use windows 7, on internet explorer I unstalled with adobe,then i've been restalling at adobe.
i'am trying to use the new one 11. whatever ! .
I need to reinstall it whenever i want to watch anything at all.
To determine if the plugin is installed and working, in IE, Click the Gear (Settings) at the top right of the browser window and choose "Manage add-ons"
In the Add-ons window you should see "Shockwave Flash Object" and it should be "Enabled". If it isn't, right click it and choose "Enable"
Sometimes (not always) if the Flash Player is downloaded and installed but not the Shockwave plugin also (http://get.adobe.com/shockwave/), the Flash Player won't play certain content.