Setting up CrashPlan with NAS drive attached to Airport Extreme

Try disconnecting all power supplies from the outlet/power source and the device. After 3 minutes hold the reset button down on the AEBS and then connect the power. Continue to hold the reset button down until the light on the front starts flashing amber fast or 5 seconds has elapsed (which ever happens first). If after the factory restore [not hard reset] that if the device doesn't turn on in a minute it's AppleCare time. The AEBS should be covered under the AppleCare Protection Plan of an Apple computer or AppleTV purchased within two years of the AEBS. If they won't swap it out for you, ask for an exception :)

Unlike the Time Capsule, the Airport Extreme doesn't support being a backup destination, no matter what drive you use. It is possible to force Time Machine to use unsupported destinations, but this is unsafe - the AEBS lacks features that help protect data, and without them, the slightest network error can make your backups useless.

Some of the technical reasons for this have been explored here: Why won't Time Machine work with a drive connected to an Airport Extreme?

However, you can look for a network-attached drive that supports Time Machine, such as WD's My Book Live. These are drives that attach by ethernet instead of USB, and they implement the file-sharing features that Time Machine requires.