Update already installed?

I have a PC/Windows Vista and use Firefox, and the Adobe Flash Player has always run fine for me. But yesterday when trying to play a game on facebook it told me I needed to update the player to the latest version. After installing it said that I already had the latest version, but after going to the help section it said that the Flash Player either wasn't installed on my PC or wasn't enabled. I went to my 'add ons' as instructed, but what I was supposed to see wasn't there. I even tried uninstalling and reinstalling the Player again, but I'm still getting the same message when I try to play a game.

I'm not sure what else I'm supposed to do, so any help or advice would be much appreciated!