One other thing to make sure of – though you may well have already but just in case – is to make sure you're plugging straight into your computer and not through a USB hub. Of course, if you already are – moot point.
I know these things can be touchy – I originally had problems getting my PitchFactor to be recognized so I could just run a software update on it. I'm running XP here myself and tried every possible thing (with the help of Eventide's support, who are awesome!).
I finally got it going using my wife's computer instead of mine. it's also running XP, but is a much newer one – I personally suspect my own older computer's USB ports might not be running at full USB2 spec so might have been part of the problem. Or not. Hard to say! :-/
But mainly, +1 to Tim's suggestion with contacting Eventide support directly if need be. When I did for my PitchFactor, they stuck with me all the way through trying everything including their suggestion to finally try the different computer, which did the trick. 🙂