Ensure you got the current Flash Player after installing XP SP3
One of my co-admin at Calendar of Updates forum is reporting that the Windows XP SP3 replaced the up-to-date flash.ocx (this is Flash Player's file and is located in C:\Windows\System32\Macromed\flash.ocx) with older version which is v6.
Users should make sure that their flash.ocx is the current version. You can run Secunia Software Inspector online or using the Secunia PSI to check what version of flash.ocx you got AFTER you've installed XP SP3.
You can also try to determine what version of Flash Player you have by going to "About Flash Player". You should see:
You have version 9,0,124,0 installed (this is currently the lastest version of Flash Player).
You can right-click also the flash.ocx located in System32\Macromed folder and check what version you got after installing SP3 of XP.