My MBWE2 (1.5TB) stopped working today while I was at work (there was a power outage and I suspect that it didn't come back on after the power was restored). When I got home, I discovered that the light wouldn't come on - and the unit (especially the top [or was it the bottom] was really hot. I unplugged, let it sit, still no light or noise when I plugged it in. I got on the internet, figured out how to disassemble the unit, took the drives out (they were still hot) and didn't see anything that looked like a problem. Discovered that you can't read just one drive on a Windows PC with the ext3 driver. So, reassembled and was going to send back to WD.
But as I was packing it up, I noticed that the AC Adapter brick was different than the ones that were shipped with my 500GB and 2TB units (I have several of these). Something (providence?) caused me to say "maybe I should switch the bricks". When I did that, the 1.5TB unit fired right up - and nothing was wrong with the unit itself.
Apparently, the brick is somehow fried or shot. The one that is shot is clearly smaller and lighter than the ones that work.
So, long story short - if your unit won't power up, check the power supply. Maybe that will be your problem.
Although I'm mad at the cheap brick that I got, at least I didn't lose 1.3TB of data!!
Hope this "story" helps someone.