(left, right or both) try another mouse. If it does react on certain clicks only, post a more exact diagnosis like what works and what doesn't work.
The relation between your problem and Flash isn't clear at all from your post. Can you tell more on that?
I try clicking on things on MySpace and I also tried to download Adobe Flash Player but my computer doesn't react when I click on some things. I have Windows XP Explorer 7.0. Thanks