I know this is an old thread.. but I thought I'd add my solution that I just stumbled upon today.
Soooo.... my WD 120GB External stopped working today which freaked me out because I had just used it to back up all my stuff whilst I dropped a new internal drive in my PC. It was working fine after the swap and I've just been pulling files off it as I needed them as to not clutter my new internal drive with unneeded stuff. (I'm OCD about hard drive space... I can't help it).
This morning however, I plugged in the old WD and it gave me the "Unrecognized" error. I tried everything: Power Management, different cables, different ports, turning it on its side, uninstalling, blah blah... nothing worked. I new it was still good because it worked in my laptop just fine.
I kept reading all over the web that it may be a power issue.. that the drive isn't getting enough to properly spin up and enumerate with the USB hub.
Then I realized I had added my printer to my newly rebuilt PC after I had used the external drive to copy some files. You see, I have this "Energy Star" HP USB printer that my dad gave me because he hated it. It really is kind of annoying because there's no easy way to turn it off when not in use.. you have to press and hold the power button like 3 times before it shuts down.
Anyway.. long story short.. I turned off the printer (which also disconnects its USB connection), replugged in the WD and it fired right up! Apparently my "Energy Star" compliant printer is drawing too much energy for my USB hub to also run my WD drive.
So, if anyone is still having trouble, try disconnecting other USB devices to allow as much juice to flow to your drive as possible.
Good luck.
