I have now the same problem with my Alienware 17 r5 ... Yesterday Dell Support Assist and said there is a drive issues so I updated it from Dell Support Assist. after finishing the laptop got heavy and the D HHD Drive disappeared... I tried multiple solutions but no one worked for me such as :

1- I saw Disk Management to solve the problem but the D disk and all its partition are not there

2- I contacted windows support team and they couldn't help me

3- I checked the BIOS settings but they were fine 

4- I reinstalled Windows 10 again ( D drive appeared for 5 minutes and then disappeared again )

5- I disassembled the D drive from the laptop and connected it again to make sure it's not a plugin problem

All these methods did not work for me... could you please help me fixing it? 

The problem is not in C drive because it works fine... the problem is in the second drive HHD D Drive which as you can see in the disk management screen shot it's not even shown so that I can assign a letter to it

First of all for your own safety and security please do not post an Email address in the forum.

It is very possibly a defective drive. You did not post whether it is an HDD or an SSD. I would suggest running diagnostics, F12 at boot, just to see if you have an error on the drive.  If you know the make and model of the drive then head to that manufacturer's web site as they all have software that can be used to check drive health. If an HDD then have you heard any clicking or unusual noises from the drive lately? From the pictures you posted I am guessing that the boot drive is around a 120GB M.2 SSD. So the   drive is either a SATA HDD or SSD.

Hi @Eng. Fares Mareai welcome to this free user-to-user Alienware laptop discussion forum. 

When fixing the OS (C:) boot partition, the DATA partition seems to have lost its partition letter so that Windows cannot see it. Please revisit Disk Management and right click on the DATA partition to assign a permanent drive letter. 

You may have to dry clean and reseat the second SSD card in its PCIe slot to reinstate its electric connection.

Please install Crystal Disk Info x64 to check health of all drives, Crystal Dew World [en] - (crystalmark.info). 

Hi sir, thanks for your replay

The hard is HHD D Drive. I ran the diagnostics but nothing appeared it said that everything is fine. do you have some solutions in mind to help me for the moment ?

Dude, do u have a RAID configuration on the BIOS storage option? Are u using RAID or NVME option?  

I have a RAID ON configuration on the BIOS