I ran into this issue recently too. I'm pretty sure they took away something from the settings screen for USB Mode/Connection or something like that.
After fighting with my computer and tablet for about an hour... I'm pretty sure what worked was to plug the tablet into the computer with the USB cable, go into device manager and find where the tablet is (I don't have it with me right now, so I can't tell you where I found it)... and then tell Device Manager to delete the device or forget it, or whatever you do to remove the installed drivers.... From there plug it back in and let it reinstall...
I don't know if there was some specific series of clicks that made it work, but I got the tablet back so that I could explore it from My Computer. I think one key is to pay attention to the system tray alerts that say its installing the drivers, click on the balloon when it comes up and says it detected the device and go through that thing and allow/enable everything along the way.
If that doesn't work, try a new USB port, I've found that it will try the whole thing over again from a different port on the computer and might be more successful with the next port.
Sorry this wasn't very technical, but I hope it helps.