Flash Player update installer does not launch

i have two PC's running Windows XP SP2.  i can download the update installers for Adobe Flash Player but when i click on them they do not launch (i think i have version 21 of Flash Player installed).  they do absolutely nothing.  they launch properly on two other PC's with the same OS.  the installers will not launch even with a clean install of the OS. any help will be appreciated, thanks!