retrieving windows license key

Your Windows 10 'key' is not like that for Win 7 or Vista. Your digital activation rights are held on MS's server. You can clean install Windows as many times as you wish; activation should be automatic based on a hash of part of your hardware id (excludes RAM and disk).

If needed there's an activation troubleshooter (Tutorial) or you can call MS's regional activation centre.

As it no longer boots, you should also check the relevant disk before installing Win 10 e.g. using a live boot disk.

Or, you can attempt to reinstall, then check your disk.

Checking your (entire) disk does NOT mean using chkdsk.. but a 3rd pary program e.g. Hard Disk Sentinel (excellent) or a basic smart check using e.g. Crystal Diskinfo.

There is also the possibility of fixing the boot problem- but that depends what's happened to your PC.

Please get as much history from him as you can. I.e. what led to this.

Then download the iso file for a live boot disk (Google, e.g. Bob Omb's, Hiren's...) and create a bootable flash drive from that e.g. using Rufus (free) - suitable instructions in Tutorial here to create a bootable drive to install Win 10.

Boot problem PC from that (to a Windows desktop). There should be a tool (check the list before downloading) to check the disk e.g. Crystal Diskinfo. Run that.

If the disk has failed... or impossible to boot PC... well... after that, assuming there's no adequate backup (is there?) it's a question of what can be recovered from the disk.

** You can also try booting it from a Win 10 install disk, via 'Repair your computer' to Advanced Boot options. One of the options is Startup Repair. (Tutorial available in searchable Tutorial section).

Running that should give some very basic clue as to the state of it. If you are VERY lucky, it might even fix the problem.

But at present, we don't know if it's O/S corruption or hardware, so first step is to determine that.

You might be able to fix it, see
Startup Repair - TenForumsTutorials
- The facility is also on the Windows installation USB.
- If you use Macrium reflect for your system images, its users have posted several times that its boot up disk's Startup repair utility is far better than Windows' ones.

Of course, if your son has been making system images routinely, the eastiest fix is likely to be restoring the last image.
my ditty - File backup vs imaging, imaging utilities, backing up drivers [post #3] - TenForums


Best of luck,
Denis

1. It will likely have the digital license as above if a regular key was input previously , or an msdm table on the motherboard, I have one like that.

If you want to save them anyway or are just curious, you can get them with winntsetup among other things

click the little blue square and select local windows installations



(i have blanked them in the pic below). Then just click the save button to save them to a text file



2. bad system config usually indicates a problem with the system hive.

you can replace the hives from a backup.


edit : corrected mistype
look in windows\system32\config\regback

or look inside a shadow copy using something like shadowcopyview
ShadowCopyView - Shadow copy viewer for Windows 10/8/7/Vista

Thanks, sensible.

ive looked in his windows\system32\regback and the file is empty

I found that MS had disabled that around the end of 1709 I think. It's possible to reenable it (Tutorial) but that's not pertinent here.

What does Startup Repair report?
A more comprehensive startup repair (FixBoot) is available on Macrium Reflect's boot disk. Please try that.

I tested the hard drive and it's healthy

- may I ask.. how did you do that?

Given what you've done, creating a live boot disk is probably only relevant inasmuch as you want to see if the PC will boot at all- which in fact you've done when running Startup Repair. However you may want to use one to retrieve data from the system disk.