Alienware 17 R3 Won't Recognize Ram Upgrade (8GB to 16GB)

I asked this question in the Dell forum, but apparently that was the wrong forum. I tried to see if the topic was moved, or even find the original topic, but I couldn't. I didn't get any notification if my topic was deleted or moved, but...hopefully I'm posting it correctly this time, as I can't find the original anywhere!

That said, I purchased an Alienware 17 R3 with tag ; it came with 8GB of RAM as two 4GB sticks. I recently wanted to updated it. I purchased two 8GB sticks of RAM that I heard were compatible (see attachment). For some reason, my laptop will read only one of the 8GB sticks. I have verified that both sticks are working by leaving only one of them in at a time. I have also verified that both sockets are working correctly by leaving only one of the sticks of RAM in it at a time.

What on earth is going on here? I'd greatly appreciate any help. Please and thank you!