Thanks for your replies. Sorry I forgot to update on this. It turns out that one of the USB cords I was using, which was not the original HTC cord, simply did not work for connecting to my laptop. I have multiple USB cords, including old ones from my old Palm cell phone that I use for my Thunderbolt. Even though some of these cords charge the Thunderbolt properly, it turns out that the same cords might not connect as a disk drive properly. So after much frustration, I swapped out the old non-compatible USB cord for the original HTC cord, and finally this worked. The lesson is this: You need to use a USB cord that is compatible for the Thunderbolt both to charge and to connect as disk drive properly. Some cords even though they fit, will only charge, but won't synch to a computer. Oh well, live and learn.