Computer hangs when booting

I have an ‘My Book Essentials 2TB’ external hard drive, which causes my computer to hang when booting up and down. The only way to stop this from happening is to disconnect it. I have read your help answer:

I went into the BIOS (with the help of my computer tech helper on the phone) and disabled the Boot from USB device  option’’ . However, I still have the problem and the tech advisor told me that the WD hard drive was not fully compatible with my new PC, Windows 7 machine. Moreover, I was told that disabling the USB Legacy Support would mean that I’d not be able to use the USB keyboard I have, so obviously don’t want to do that. It seems that I have no option but to unplug the WD My Book Essentilas HD every time I use the computer, which is very frustrating! Unless I can get round this problem I think I’ll have to return the unit to the shop and ask for a refund.

I know you tried disabling boot from USB did you try moving the USB after the main HD?