I am having the same problem but I am using a ITB Home Book . It doesn't matter which Windows OPS I use, (XP.Vista, Win 7) I have exactly the same problem booting up. The only way around it, is by switching the hard drive ON/Off and wait until it completes booting up. Pain in the Arse.
There are other problems with this drive aside from booting up. I've already had to replace power supply and the software installed with the drive interferes with other software applications particularly when it goes into hibernation. When the drive goes into hibernation software hangs requiring software to be closed. Windows doesn't recognise drive. Drive won't switch off and at times will not turn on. Drive goes into hibernation and won't come out of hibernation. WD really need to pull their fingers out and start doing something about these problems. I have decided to transfer all my data to a Seagate drive and return the WD. No one should have to go through this.