WD My Book hangs my PC on boot up

WD External Drives External Drives for PC
4

I’m having the same problem on a Vista PC.  If the drive is disconnected, it boots up perfectly.  If the drive is connected and turned on, the computer never gets to the little scrolling indicator that shows Vista is loading.  If I shut down and restart again with the drive connected, the computer gives the failed to start message, does a scan, finds nothing wrong and prompts me to do a system restore.  Again, I unplug the drive and it boots right up.