I returned my last Harddrive (same power issue) and got a warranty one that after 2 weeks, developed the same problem.
I figured the solution out of luck. This is because I use my hardrive on both macs and pcs.
So this is how I figured out the problem.
You know how it has a firewire output and a USB Mini-b (5-pin) output.
Well, when I plugged only the firewire into the Mac, it was not enough to power it up. BUT, then I plugged in BOTH cords to the mac and it powered up!!! Unfortunatley, THIS does not help if you are using a PC since PCs do NOT have firewire inputs!!
I noticed my teacher had a hardrive. He had the same two outputs (a firewire and the USB Mini-b (5 pin) output.)
He had this cool wire that on ONE end, the USB mini-b 5 pin (to connect to the harddrive.) On the other end of the wire, it had TWO USB ends! (split)
This way, you could plug your harddrive in with two USB ends into your PC computer. All of a sudden, this seems to be enough power to power up your harddrive!!!
It really **bleep** that WD is not realizing they are not making their devices easy to power. Their built in power supplies easilly lose ability to recieve nessisary power after first time use, especially if you are going in between mac and PC computers.
SO, if you dont feel like taking the time to keep using your WD warranty, then go on Ebay and order one of these:
THIS should help be enough power to power up the harddrive for your PCS (and Macs)!
Hopefully this helps.
And Dear WD, you need to fix this issue. Thank you