What browser are you using? The player on Word Nerds (I didn’t check the others) appears to be a Flash-based player, so you need to have Flash enabled in your browser. I normally use Firefox, but have Flash turned off by default. I can usually click on the button to enable it, but for some reason it didn’t work in my browser. I could, however, play it in IE.
IANACE (I am not a computer expert), but that’s my WAG – Flash not enabled in your browser.