This all started when I got an Alienware 15 R3 last year. Here is what I have done over the course of a year in order:
1. I took the HDD out of the Alienware and replaced it with a 1TB SATA SSD. I never once turned on MS Windows 10. I wrote "AW" on the HDD with a marker and put it in a drawer—I had plans for it right from the start.
2. I installed Linux Mint Cinnamon.
3. I bought an M.2 SATA 3 SSD last night and put it in the machine (there are slots for a total of four SSDs). I installed Linux Mint on it.
4. I cloned the original HDD (that came with the Alienware) to the 1TB SATA SSD I mentioned above.
5. I put the cloned 1TB SATA SSD into the proper slot and turned the machine on.
6. I was unable boot up into Windows but I can boot up into Linux just fine.
I thought it had something to do with UEFI vs. Legacy and/or secure boot vs. unsecured but I changed all of that stuff in the BIOS in every way imaginable to no avail.
I thought what would happen would be that I'd turn the machine on, go to grub, and see an option for logging onto either LM19 or W10. I don't see that option nor do I see any other way to log onto Windows. Of course, I can see the other hard drive from Linux and everything looks good. It looks like a typical Windows C or D drive (or whatever it is).
Ordinarily, I wouldn't worry about it this much, but I need W10 for school and work and I use Linux for everything else.