My guess is that you had hook installed. When in the PSJB app on ti-84 there is an option to install, this makes it so that any usb that tries to enumerate the device will have the exploit automatically sent to it. Your computer is obviously not susceptible to the exploit while at the same time, it will simply not see the calculator while hook is installed. So I have to always remember to press 3 to uninstall the hook, then hook up to the computer, then press 2 to reinstall hook after I am all done. I don't know if this is exactly what happens to you but I hope it helps.
And on a side note, this little key does look cool to have. Every now and then the ti-84's ram will reset (brandon wilson warned of this) and I will have to change all my settings again before using it. A little chip like this seems like it would be very maintenance free.

