There are a number of ways to approach this. Hopefully the data on the drive is not encrypted. For a Windows 10 computer you can force Advanced Boot Options.
Hold the Power Button for 5 seconds or until the computer completely shuts off.
Press the Power Button to turn the computer on.
As soon as you see the rotating loading circle, press and hold the Power Button until the computer shuts off.
Repeat this process 2 or 3 times until you see the Preparing Automatic Repair screen.
Let the computer boot to the Automatic Repair screen.
Click Advanced Options, and then select Troubleshoot
You want to get the option to open a command prompt. At the command prompt type
netuser administrator /active:yes
This will enable the Hidden Administrator Account. This account will let you access any other account on the computer.
If the above command does not work you can do it offline per this guide. Hopefully it works for Windows 10. In order to boot this disk SecureBoot needs to be disabled in UEFI settings if the computer was pre-installed with Windows 8 or 10. Also CSM or Legacy Boot should be enabled. If there is a Quickboot or Fastboot setting that should also be disabled. You can burn the iso of the utility on a Windows 7 or higher computer by right clicking the iso file and selecting Burn Disk Image. There is a later version of the utility here than what is shown in the guide.
Another method of enabling the hidden Administrator Account is to edit the registry offline per this guide. It's for Windows 7 but the same steps are good for Windows 10. You can use a install disk of Windows 10 using the media creation Tool. Boot the disk and at the first window asking for language press Shift + F10 to open a command prompt. In the guide it says to use the command %windir%\system32\config\SAM. Do not use this command. Simply browse to the SAM directory on the internal C: drive.
Last option would be to boot a live linux disk like Ubuntu or Mint and copy the files to a USB external drive. Because Windows 10 does not have a normal shutdown there may be a problem trying to mount the partitions. You may need to boot the Windows 10 disk, access a command prompt and type the following command
powercfg -h off
Burn the iso to a DVD. If you need instructions on creating a bootable USB flash drive instead of a DVD post back.
Hope this helps. Edit: If all else fails you can pull the drive and attach it to another computer using a USB adapter.
Edited by JohnC_21, 18 November 2016 - 07:46 PM.