Several clicks

Hello,
I'm having trouble with flash applications (specifically the ones from myspace).
I have to click several times in order for anything to occur, Firefox stops responding and the screen flashes white when I click.
This had never happened to me on this computer but I've had the same problem on a laptop.
I tried other mouses, Internet Explorer, running the anti-virus but I had no results, it seems to work fine on windows XP though...
What can it be?