Same thing happened to me once. I was bummed that i lost a drive and trying to figure out what to do. By chance tried a power supply from another identical drive and it worked.
For future reference, if a drive truly is dying but not all the way there yet you can sometimes get them to come back to life temporarily by putting them in the freezer for a while. A buddy at work had a drive with a bunch of media on it that he didn't have backed up because he could re-rip but it would be a pain. He did a couple cycles of freezing the drive and transferring data and got pretty much everything off of it.
On the backup front, I've been using Carbonite for a while and like the simplicity and little green dot on windows which tells me if a file is backed-up or not but the way they throttle uploads once your backup set gets big doesn't work for large media collections like I have (and presume many on this board do).
Crashplan doesn't seem to throttle, or at least not as much and I've been able to get more than a terabyte uploaded in just a few weeks. I'm planning to let my Carbonite subscription for at least my main audio/video workstation expire and move entirely to Crashplan for it. It will also back up external drives which carbonite will only do in limited situations.
I won't go so far as to say a file doesn't exist if it's not backed up because I can prove that wrong
, but I will say that if you aren't backing something up it must not be very important and clearly you'd be fine if you lost it forever because it's just a matter of time.