windows7 pro boot failure with my book 4t

windows 7 pro reboot failes … with my book 4t attached … also have 2t my passport attached and runs fine??

It may be possible for your computer to switch priority to your WD My Book while booting. Try disabling legacy USB support in your BIOS. If this is not possible then you may have to disconnect your unit before restarting or shutting down your system.