Area-51 R5, Five drive support?

Five should work. The "Alienware Area-51 R5 Setup and Specifications" PDF states for internal drives =
* Three 3.5-inch drive bays for SATA hard drives
* Two 2.5-inch drive bays for SATA solid-state drives or U.2 solid-state drives
* Max up to total five hard drives supported

Have you tried powering off, disconnecting the SATA cables from the motherboard for the three mechanical drives D, E, and F. Leaving only the C: drive and the SSD drive, then booting into the BIOS to see what is shown for drives?

Sounds like it's just a SATA-3/600 SSD, so ...

First hurdle is that it should appear in BIOS.

Then, in Windows-10 Disk Management it should ask to be Initialized. However, it needs to be RAW/uninitialized for that to happen. DiskPart can erase it.

I just added 2 additional 2.5” SSDs a few days ago,  making the total 4 drives (including the on-board M.2). All I needed to do was go to Disk Manager and format each SSD. Everything was normal after that.

In fact, I originally checked in the EFI BIOS and didn’t see where to add/config the drives.

Bradleyjs2,
He states, "Windows does not see it.". Are you saying that your drives were also "not seen" in the BIOS or Device Manager, yet, the Windows 10 Disk Manager did identify them?

Update.

I moved the SSD from the small SSD cage to one of the regular 3 drive cages and used one of those connectors.  The bios and Windows see's the SSD drive, works perfectly.

Moved it back to the all in one connector from the smaller SSD cage.  Nothing, sees it, neither the bios or windows.  I followed the all in one connectors and they are connected to the motherboard under the video card.

And you removed the video card and reseated cabling to the connector?

Yes Sir, I did reseat the connector. Still nothing

I had the same identical problem. And I moved them to the 3.5” and connectors and it showed up in Disk Manager. I bought a 2.5” double caddy and mounted it in the 3.5” and all is well.

You are using 5 drives?  I don't know how.  4 is no issue, adding the 5th or 6th is.  I don't know how you are able to split the connectors to make it work.  Can you take a picture?

Well this is not good.  Can't over clock the system anymore.  Since I swapped drives around it trashed this file

AREA-51-R4_Intel-Turbo-Boost-Max-Technology-Application_6MW47_WIN64_1.0.0.1033_A00

Getting ITBM Driver not available, Exiting application

Did an uninstall, reboot, reinstall and still not loading

I have a 1 Tb M.2 2280 for boot drive and three WD Black 4Tb hard drives in Raid 0. I attempted to install a Intel 905p 480gb u.2 ssd and it did not show up in bios or disk management. I then took a San Disk 2.5 ssd and installed it to see if it would work and it did! Is the 480gb u.2 compatible? 

The problem seems to be that there are five bays ... three 3.5" and two 2.5" ... and there are six SATA power connectors, although it would be a real feat to make the power connectors reach the five bays as configured.

BUT ... there are only four SATA data cables. That appears to be all the motherboard supports. So if you are going to install five hard drive, at least one of the SSDs is going to have to be U.2.

Did you manage to get the U.2 drive to show up?

I'm having the same issue.