The USB serial chip on the Axon/II should show up in the Device Manager regardless of whether it's powered on. I forget what it shows up as, but open Device Manager, then plug in the Axon. Device Manager will refresh its listing when you plug in the Axon.
Actually now that I read your post again, I think someone else did the same thing a couple of months ago, and in fact fried the USB-UART chip because they're both on the 3.3 V line, or something. I can't find the thread, though...
One option is to use a hardware programmer, if you have one. If not, the $20 one from Pololu is a nice and cheap one to get. The other option, iirc, was replacing that tiny surface mount IC. Admin will know more and show up, eventually, I'm sure
Edit: Not the thread I was thinking of, but same situation: http://www.societyofrobots.com/robotforum/index.php?topic=10263.0