I would suggest you guys to uninstall Flash Player completely as the Ie addon or your browser's addon. Look for the Application data and registries for it and delete them. Then after this process Restart your pc. Go to youtube open up a video. And it will say get the latest flash bla bla... Open up the link and install it. And try if it works by then.
If it is still the same check other sites that has flash videos such as like metacafe or msn videos.
If the problem not occurs. Delete your browser's history, cookies, temporary net files. Try reopening it.
If the problem occurs Try Another browser if there is still the same problem but Im sure there wont because every browser has its addon installed just for itself so If it works properly at least try to move on to the browser that works
Thats Only I came p with Hopefully I have been helpful tho. Good Luck with it guys.
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