Issues putting a hard drive in the optical bay of my early 2011 MacBook Pro

I'm asking for help for my brother! I recently switched over to a dual hard-drive setup, and it worked perfectly. However, my brother is having issues.

First off, here is the hard drive we are trying to put in, using this caddy. Both worked perfectly when doing this to my computer. If we can get this HDD to work, we'd like to put this SSD in the main hard drive bay.

He has an early 2011 15" MacBook Pro. We read up online, and people said that the optical bay for his model only has SATA II, while the main bay has SATA III, which means he should put his HDD in the optical bay, and the SSD in the main bay. He wants to put the HDD in the optical drive area, and then transfer everything over to the new HDD, before putting the SSD into the main bay.

The issue is that when we put the HDD in the optical bay, the computer can basically not recognize or use it. If plug the HDD in via a usb cord, he can initialize it and erase it to Mac OSX Extended (Journaled) perfectly fine. It only takes a few seconds, and as far as I can tell, it works. However, when he actually puts the hard drive in the optical bay, it either doesn't show up in disk utility, or it shows up, but can't be accessed or changed.

We left it in, and it showed up after 30 minutes or so. When he tried to initialize it, however, the computer said it'd take 5 hours to do. The progress bar ended up getting half way done, and then stopping, so that didn't even work.

We thought that maybe it could be a firmware issue due to this post that we found, but we looked and definitely have the newest firmware version (2.7, I believe). Also, I don't think that thread applies to us, since we aren't even beginning to deal with the SSD yet, just the HDD.

We also tried just initializing it before putting it into the computer, but the computer doesn't seem to recognize it correctly. The name is changed from "New HDD" to "disk1s1", and we can't actually access it. That's when we tried initializing it again, just for the progress bar to get stuck.

Looking online, this setup should work. Tons of people have done it, even using the hard drive we are using. We aren't even trying to put a SSD in yet, which is where most people have problems with the 2011 model. This is just a regular hard drive! I don't understand what could be wrong, and could use some help!

If there's anywhere else you think I should post this, just let me know!

Thank you!