Installing new Hard Drive question.

(The computer I'm using to access this forum is not the one I registered with--that machine is the one I'm referring to here.)

The hard drive on my Dell XPS 8500 (circa 2012) now seems to be toast. The latest blue screen says "unmountable hard drive".
I think it has the original BIOS, EFI, and has only been on internet once since I've owned it.
However; I have some info that has confused me recently. I paid for a disc from "EasyRE" Easy restore; and that seems to have
made things worse. They have this tool whose page I think I got the following notion from, below this link I've typed in.
Windows 10 Embedded Product Key Tool

My intention is to put a new hard drive in. The machine came with Win8 installed, and no DVD for the hard drive. (an OS disc).
So what I've learned is that the license for the original OS is stored on the MOBO.
So, my idea is that if I simply put a new hard drive in, then, I could do either of two things:
1. use the system restore discs I created, when the machine was new, that the OS prompted me to make.
I'm assuming that the original license key will help reinstall the OS?
2. I also have recently purchased a used "full version" of Win8.1--and I don't know if the stored "old" license will interfere with installing 8.1,
somehow.

As you can probably tell, I'm not too well schooled on everything computer. I messed the XPS up trying to make it a double boot system,
and should have listened to a couple of friends who said, everyone they know that's tried that has failed.

Anyway, any help appreciated. (And yes, the "new" hard drive is SATA, with specs likely close to the old one.)

Install the New Hard Drive, and clean install Windows 10 with the Generic Key - once the PC goes Online it will receive a Digital License Key from the prior activation of windows 10...
Or clean install windows 8/8.1 - it will install using the Key embedded in the BIOS - then upgrade to Windows 10

I see. So a Windows key is a Windows key, and it doesn't matter what version you're installing--even a newer OS?

The reason I want to use Win8 is that I'm thinking some of the many programs I have won't cooperate with Windows, even with using the compatibility wizard--or equivalent.

But this eases my mind. I've had this drive failure come on very slowly, and have been trying to deal with it for the better part of a year. I really don't want to lose
files/programs and whatever else is on the 1TB drive in the XPS...so much room, it's easy to forget what's on it. i did manage to back up my own files--but I'm not
positive I got them all, and that effort came many months before It went badly awry. So the links you provided might be worth a try, in that regard as well.

But I do have one more question. Does "UNMOUNTABLE_BOOT_VOLUME" pertain to the hard drive, since it doesn't seem to work--which seems self explanatory;
or does it apply to the Bios/UEFI's ability--or not--to fetch either a fix or OS from a DVD--since that's what I've set the first boot option to now? "Unmoutable"
suggests you can't "mount" anything on the old drive. Yeah, dumb question, I guess.

Excuse me, I meant "...won't cooperate with NEWER versions of Windows."

Oh great, I just booted up the XPS a few times...I have to shut it down with the power button when the blue screen appears "your computer has run into a problem, etc.",
and a moment ago it shut itself off. So when I just hit power again, there's no monitor signal and it's beeping four times in a row, pausing, and then repeating four beeps.
The light in the power button is amber. Has the battery given out?

I've attached a picture file after getting this to open pressing F12 (F8?); but possibly this isn't relevant. But then, as I say soon after turning it on again, the above happened.

I have an XPS 8500 as well that i'm on right now. Below is one solution to 4 beeps pause 4 beeps. Older Machines could very well have a worn out battery which is usually easy to replace. You should really check the health of that WD10EZEX-75ZF5A0 1TB spinning hard drive before anything else, it might be failing. Some how stick it into another machine via a dock or usb enclosure and get the CrystalDiskInfo utility to check it. If you had another PC it would probably have another 3.5 big hard drive slot just waiting with an extra two SATA cables, one wider, the other narrow, just like how it is already as an example. Make sure the Computer is powered down and unplugged from the wall of course, then press the power key for 15 seconds to discharge. Discharge your own static electricity by touching anything grounded metal first.

The UNMOUNTABLE_BOOT_VOLUME could very well be that the Hard Drive in question is formatted in NTFS/MBR and your bios is in UEFI mode. It would be necessary to have your Hard Drive formatted in FAT32/GPT to work with UEFI. This would necessitate using another machine and formatting it this way. Your screenshot shows: OTHER OPTIONS: (at the bottom) - If you were content to use legacy mode with less security features, you could arrow down to: Change Boot Mode Setting - and look for a setting to turn off UEFI enabling legacy BIOS mode. That may solve the issue straight away.

On this XPS the bios boot up key is F2 and the boot options key is F12. Since your hard disk is booting 1st in the BIOS, you'd have to key up F12 at startup to be able to select the CD/DVD to boot from your install disks. If you're installing the exact same OS (8 or 8.1 - make sure which: Home, Pro, etc.) the embedded product key will auto register - I don't believe 8.1 will register if it came with 8, you could try - some one else here may know, i've never had to do this and cannot be readily found on the net. If not you can then upgrade the original 8 with 8.1. Nirsoft has a BIOS OEM product key finder without having to register an account (produkey). Hope this helps.

No response since Feb '22 ???
What happened?