Help! Drive not mounting on Mountain Lion

My “WD My Book Studio” has been working perfectly since I bought it back in September… That is, until tonight.

I was away from the computer (Intel iMac running 10.8.2) for a little while, and when I came back - I noticed that “TheVault” (the name of the external drive) icon was grayed out on the desktop.  I thought that was weird, so I tried ejecting it (didn’t do anything), so I restarted the computer.

Now, WD Quick View launches with the computer, and claims that the drive is OK (temperature OK, 34% space available, et cetera), BUT I cannot get the drive to actually mount in Finder!  It does appear in the Disk Utility, but there is some weirdness there too.  In the My Book tab, I cannot repair the disk, even though it is an external and not running the OS.  In the “TheVault” tab, I can run “Repair Disk” which runs successfully and claims that the drive is completely fine - but still doesn’t mount!

I’ve tried connecting the drive to the computer both via FireWire (what I was using previously), and now USB.  In both cases I get the same result.

Please help!  Our baby is just four months old and we have been keeping all of our photos on the volume. I really hope the data is recoverable!

A new oddity: I can see all of the files if I use Terminal and navigate to \Volumes\TheVault\ - so I hope my data is actually safe!  But why isn’t it mounting properly in Finder?