You can't assign ptt to a button? Now that is weird. Mine is the big red 'fire' button.
There's obviously something amiss there, but I'm afraid I'm out of suggestions.
I know that I did have some software issues at first which took some sorting out, and I'm still pretty convinced it'll be something to do with software rather than the stick.
Such a shame when crap like this spoils your fun, eh?
P.S. This is really obvious, but you have made 100% sure of all connections? Tried a different usb port? Made sure it has a dedicated port and not thru a hub? Sorry again if patronising!