Upgrade to Windows 10 failed with Black Screen

Not sure if this should be in TenForum. Have registered there just in case but i feel more at home here!
A friend of mine fell into the "Your update to Windows 10 (from 7) eill take place in 5min 32secs. He is adament that he did not see the line "Reschedule or cancel Update". He just hit the "X" at top right. Unfortunately he didn't realise that the update would take place in the background. A bit insidious this I think.
Anyway Windows 10 did work to start with although he lost his wireless connection. I said this was probably a wifi driver. So I told him to connect via a LAN cable and that worked. After rebooting a coou[ple of time the balck screen problem started. I now have my friends laptop to try to solve the prolem for him. On switching on machine Tthe Win 10 logo shows, after a few moments a message comes up "Windows has encountered a problem and nned to restart. Below it reads For further info on the problem see "UNMOUNTABLE BOOT VOLUMN" It restarts automatically with the message " Preparing automatic repair" That goes off sfter a moment and then the black screen jusst hans. No apparent movement anywhere.
I would like to get this laptop back to it's fully working Windows 7 state if possible. I have tried to use Linux mint to get into the HD to save the data files but no luck . It seems that the HD is now unmountable.
Any help or ideas very gratefully welcome.
As an extra whereas for years we have been able to boot into Windows Safe mode from the BIOS flash screen by pressing F8 or similar you can't do this in Windows 10. It seems that you must already be in Windows 10 before you can boot to Safe mode. Bit pointless that, I think!

Unfortunately you crash it multiple times so you get the problem screen then you follow advanced recovery options and pick recovery then pick go back to previous version of windows if it has not been 30 days yet.
Advanced Startup Options - Boot to in Windows 10 - Windows 10 Forums
Windows 10 - Go Back to Previous Windows - Windows 10 Forums
Good Luck

Thanks for the response. Unfortunately all I get is the same "Preparing Automatic Repair" then a blank screen!

Wow, even after hard crashing it? Try taking out the power and battery for a bit then doing it, it may be off but doing the hybrid-off (fast start) thing.

Thanks again but to no avail, I'm afraid. Same result just keeps going to Preparing Auto Repair then blank screen!

You might be able to copy the folders the upgrade made of 7 then clean install 7 and put those folders back (worth a shot) then reboot and try to use it to roll back. Grab the folders with something like parted magic or an ubuntu live distro. Also if you can before messing with it if you have the space I would image the drive as it is now with a bootable macrium reflect so you have a fallback to square one if needed.

http://www.thewindowsclub.com/rollba...-after-30-days (the files are hidden)

Think I have got the answer here. I have just remembered that I introduced my friend to Macrium Reflect a while ago and showed him how to create a backup image of the whole disc. I have found on his external HD the fruits of my labour inso far as a backup dated just last March. He has most of his data since then backed up to an external HD so tomorrow I will use the Reflect to restore to A date in March so not too much trouble, I hope! There is a small app that you can install to stop the Win 10 badgering so I will install that if I can find it. Many thanks for your help. Will report back on progress.

If they have 7 pro you can use the second one on this list then group policy will keep windows update from upgrading the OS. Otherwise use option one and create that dword with that value and same thing happens.

Subkey: HKLM\Software\Policies\Microsoft\Windows\Gwx
DWORD value: DisableGwx = 1

This one only off GPO (that's how i'm using it on 2008 R2 server)
Subkey: HKLM\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate
DWORD value: DisableOSUpgrade = 1

Thanks very much for this.My friend has Windows 7 Home premium so it needs the first option, I assume? I'm no expert with the registry, I tend to avoid it if I can. I will make a registry backup first then exactly what do I do to insert this entry?

If your not comfortable doing it you can use this to do it for you and this will also remove the old win ten files if any are downloaded already. Never Ten (https://www.grc.com/never10.htm)

I also made a .reg for you if you want to just use it. Make sure to run it as admin.