Hi [NAME] welcome to this user to user discussion forum. This is not Dell Support.  Seems you are saying that your OS(C:) boot drive is the slow SATA HDD?  Alienware 17 R5 accepts fast and ultrafast M.2 PCIe Gen3 x4 NVMe cards and when this NVMe card is the OS(C:) boot drive, performance will be significantly increased. The 1TB and 2TB M.2 NVMe cards usually provide the best read/write speeds, see database within Crucial System Advisor Tool Here. You do not have to get Crucial M.2 cards, users have purchased Samsung M.2 cards. Getting a good deal on Amazon, eBay, etc. is always worth looking for discounted offerings.  The NVMe OS(C:) boot drive should be ultrafast option to get the best Alienware 17 R5 performance. The M.2 card should be created with GPT partition format, and then BIOS Boot list option UEFI enabled to get all the modern reliability and security features.  Install Windows 10, How to create a bootable flash drive for installing Windows 10 in the UEFI mode | Dell US  Your Windows 10 should be licenced automatically online by Microsoft data base.  If the HDD has just lost the Windows operating system, make it a Data drive and perhaps all your personal files will be available. Crystal Disk Info x64 is a good utility to check drive status. The 2.5-inch bay will only accept slow SATA drives.  Please click on Kudos to say thank you for response from user that is not employed by Dell. Please share an update on progress, so that other users derive benefit from your experience. Thank you. 
Would appreciate if anyone can help with suggestions. A week ago my 17 R5 failed to boot up, I tried using the Alienware option to re-setup Window, and it keeps re-installed until it reaches around ~80% complete and stuck there. It wont allow me to select the reset to factory default option. When I use the Alienware tool to run diagnosis, it said the HDD has issue. Since my 17 R5 warranty has expired, I was thinking if I should just replace the HDD myself, but I am not sure if by doing so, the Alienware tools/Window installation files in existing HDD partition can be extracted still? Anyone has any experience in similar issue ? I tried the Dell support in HK, its really sad, took me 4 tries to reach tech support and found out there is no repair center in HK. They claim will give me a quote on possible HDD replacement fee, but I have lost my confidence by the way the tech support sound.
17 R5, HDD died, HDD replacement, OS reinstall issues