My Book Essential USB2.0 won't allow me to boot my Windows 7 when it is plugged in

I just purchased this external drive and everything seems to be working fine. Whenever I try to boot my computer with My Book on my computer refuses to start Windows 7. If I unplug My Book it boots fine. Any help would be appreciated.

I have the same problem.  However, I have had the MyBook Essential for about 6 months without a problem.  Then yesterday my computer would not boot.  After the opening Bios screen, before Windows starts to launch, it would turn to a black screen with just a blinking cursor.  Then I unplugged the MyBook Essential and it booted.  Then plugged it in again and it won’t boot.  I suspect the drive updated its driver or software automatically or something, and created a problem that did not exist before.  I’d love to hear if other are having this problem, and if there is a solution.