@oldpueblo, did you ever resolve this? My I got my Lumia 920 yesterday, plugged it in, and it appeared fine. (Win8 Pro as well). Today, no luck. In Devices and Printers, it shows a Lumia 920, but it is listed as "offline". I deleted the device from Windows, and tried again - still didn't work.
I just unplugged the phone, turned it off and back on, and when I plugged it back in Windows recognized and re-installed it. Now it's available again.