disk utility won't erase external hard drive

Good morning,

Noob here. I'm trying to erase my external hard drive, a Toshiba 6TB Canvio Desktop External Hard drive (model # HDWC260XK3J1) with disk utility with no luck. The hard drive has failed (a different problem) so I have to return it to the manufacturer for a replacement, which means I can't just take a hammer to it like I'd like to.

My computer is a 13 inch macbook pro, mid 2009, and I'm running El Capitan 10.11.1.

I was able to erase the secondary (HooliDisk2) but not the primary (Toshiba External USB 3.0 media) external hard drive. I have tried erasing it, left it on for hours (12+) and there seemed to be no progress made. I am trying to partition it now with the same problem. First it won't let me partition, then I have no idea how but I'll click something and it the 'apply' button will enable; but even that doesn't do anything. 't doesn't seem to be mounted, and I've tried to mount it with no success. I'm not able to mount the primary drive (the toshiba) as I don't have the option to do so, it's greyed out. The secondary drive (HooliDisk2) has the option to be mounted but it won't actually mount.

I'm attaching some screenshots so you can better see what I'm talking about.

This is my primary external hard drive:

This is the secondary drive:

This is what happens when I try to partition this disk:

And this is what happens when I try to erase it:

Thanks in advance for your help!