Why flash 10.1 is not working in my computer?

I don’t know the exact reason behind this from last two days my flash 10.1 is not working. Every time I am trying to watch online video an error message just pop up check you flash player. I have tried to fix this problem by reinstalling my flash player but my problem is still the same. So I want to ask this from you guys, what may be the reason behind this problem? And how can I fix this problem?