I had such a battle with my Airport Extreme and WD External HD....It worked beautifully the first time until I disconnected it to bring it somewhere then plugged it back in when I returned home. It didn't pop up on the desktop as it did the first time! I tried restarting, reseting the AE, all kinds of things with no success. When I opened the Airport Utility, the WD was listed under "Disks" but still hadn't shown up on my desktop. The solution I found was to open the AE Disk Utility and check the box that says something like "Show available disks in toolbar". A little icon appears on the bar by the clock/battery/wireless signal icon. If you have your HD plugged into the AE and it's not coming up, click on this box and select your HD from the drop down. I have password protection on it so I just put in the pw and it pops up on my desktop. Hope this helps.