I completely lost my LaCie hard drive last night. It wasn't appearing on the desktop, and when I checked in System Profiler, it wasn't appearing either. After the tightening in my chest and tingling sensation went from my arm, I found an article which suggested I unplug the drive and zap the PRAM, and then once it was rebooted, reconnect the drive. I tried this, but it didn't work.
Then I read that I should unplug the drive, turn off and unplug the computer, leave it for 10 minutes, then turn the computer back on and reconnect the drive. I tried this for 30 minutes, and still nothing. So I turned it all off and unplugged it at the wall and went to bed, thinking I had lost all the work which was on my storage device. When I woke up, I plugged the computer back in with the drive still connected to the computer, and amazingly, there it was on the desktop!
Now, the desktop did have problems (the menubar icons were missing from the top right corner of the screen, and everything was running strangely), but once I had unmounted the drive properly and done a restart and connected the drive again, it all worked fine.
Don't give up. Try my approach if you lose your drive. Sleep on it!
[robg adds: Offered as One Last Hope for those who may have a hard drive that seems beyond recovery...and yet another great reason to ask yourself that key question: "Have I backed up lately?"]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20070117235241862