Hi [NAME]  there are two keyboard vendors for Alienware 17 R4 laptops, and these vendors have their own unique type of key hinge clip. How to identify DC16 & DC61 key hinge clip is explained Here. Getting the replacement key and installation should then be easy.  Dell warranty support for your Alienware 17 R4 laptop might not be possible, please go to Warranty and Service Extension - Dell Community  If prefer to install new keyboard, use your Service Tab Here to see which keyboard is already installed, and if this or other replacement keyboard is wanted.  If there are no local repair shops, please consider How to arrange an 'Out of Warranty' repair on your Dell System | Dell US  and  $100 Dell Laptop Repair | Dell Repair | Laptop Repair | Notebook Service Center (parts-people.com).  [This user does not work for Dell and volunteers their free time. Please remember to say thank you by clicking on Kudos as this user's only reward.] 
I have the same problem on an otherwise perfect condition Alienware 17 R4.  The "N" key will not function but on a USB keyboard, it works fine.  I did take apart my two previous laptops but have not yet disassembled the Alienware.  This is an expensive laptop so I wonder why the keyboard problems? System has the Intel i7-7820 cpu.  Also the keyboard does NOT function when booted directly into BIOS (using F2 at startup), thus it's apparently more than a Windows reinstall driver issue. I've found that sticking the little screws thru a sheet of paper with the panel layout drawn on it helps keeping track of which one goes where.
17 R4, keyboard keys not working, #4