I was downloading from the installation problems page for Windows. Installation problems | Flash Player | Windows 7 and earlier
But i found way to use it by downloading from here Where can I find the "Extended Support Release" of Flash Player for Windows or Macintosh?
Not sure what the difference is but one works and one doesn't. Anyway thanks for the help.
The Extended Support Release is not the latest version. It's version 18 and only contains security fixes and does not contain any other bug fixes or new features.
Is there an error message when you try to open the version 20 file (the one downloaded from the help page)? What version of Firefox are you using? What Service Pack is installed on your XP system?