What you bought is ecc ram, wrong ram for your machine.
Get a 16GB kit from crucial.
http://www.crucial.com/usa/en/compatible-upgrade-for/Alienware/alienware-x51-r2
Or one of these should work.
https://www.newegg.com/Product/ProductList.aspx?Submit=ENE&IsNodeId=1&N=100007611%20601190327%20600006072%20600551103
My Alienware x51 R2 currently has 2 x 4 GB of RAM (8 total), so I went online and purchased 2 x 8 GB of DDR3 RAM (16GB) and put the chips in. I power the unit up and it just beeps at me, clearly not liking the new RAM chips.
These are the chips I purchased
(https://jet.com/product/16gb-2x8gb-Memory-Ram-4-Ibm-System-X3650-M3-7945-Ddr3-pc133-Ecc-Register-by-CMS/1f206f2823e149dcbc8b6af560b89caf)
I put the old ones back in and here I am now trying to figure out where I went wrong. Help me please, guys?

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