Can't boot if USB external drive attached

Well this has been a long, very long old gathering of old post. Thank you for letting us know how you fixed your problem. I will remember your trick.
Welcome to our forum.

Hmmmmmmm, seems like a weirdy. I had a 500 MB Seagate external on my HP quad core. Kept having to unplug it on boot or it would hang the machine until I did. Plugged the same thing into my HP dual core and it gave me no hassle. Maybe it's the particular USB port? Or maybe one machine likes me more than the other?

Interaction with Network Drive???

I have the same problem with a 3 year old HP Pavilion Desktop - AMD quad core processor running Win 7/64.

I tried updating the BIOS, first to put the USB last in the chain, then to mark both USB and Network as disabled so it will only boot to HDD or DVD. Still freezes (black screen with blinking cursor) during boot.

Strangely enough, I used to have a problem with my Seagate network drive not connecting when the computer booted. I bought the WD because I got tired of having to jump through hoops to access my network storage every freaking time. Now that I have the stupid WD drive with THIS problem, my Seagate network drive connects every time!

Can't be a coincidence. Does that give anyone an idea???
Could it be the WD Unlocker, which shows up in Explorer as CD Drive (L WD Unlocker?