We have seen a number of reports like yours in recent weeks, and there may be a simple solution.

Go here: http://www.adobe.com/software/flash/about/

If your current Flash Player version works, (doesn't matter which browser), you should see a brief animation and then "Adobe Flash Player Successfully installed".

If you do, right click that animated image and select Settings. Then remove the tick for "Allow hardware acceleration". Click Close.

Try any Flash videos now.

If it works in the browser you did this in, it should also work in other browsers without further action.

Hope that helps.