Disk Utility not loading when external hard drive is plugged in.

So I've been having some issues with my external hard drive the past few days. One of its partitions (BACK UP) was not appearing on my desktop so I wanted to try the "Mount" function and attempt a remount of the drive. However, when I try to open Disk Utility, it does not load. It simply says "Loading disks" (image below) and does not change. The strange thing is, this only happens when my external hard drive is plugged in. When it's not, Disk Utility works fine. Any suggestions as it how I could fix this?

Also, I have backed up my files elsewhere so losing everything on the hard drive won't be an issue.