Now, this is of course only works if you have physical access to the computer and a re-installation or repair disc of preferably Windows 10.
First you must create a bootable USB of the Windows ISO, which can be done here: Rufus Download
After the repair bootable has been created, boot from the USB and arrive at the Windows set up screen. From here, you will press the shift+F10 to open up the command prompt. This prompt has administrative privileges and will allow you to access the files in the already installed Windows OS.
Note: Please make sure that UEFI secure boot is disabled, if needed please change the boot sequence.
Now from here, you have to find the drive letter of the installed OS, normally it remains the C: drive, but every once in a while this changes. You can use the dir command to search through each letter and see if the directory displays. However, you can also use the diskpart utility with the command list volume to get a sense of the volumes and the letters attached.
X:\Sources> dir a:
DISKPART> list volume
After you find the operating system, you then want to copy over the sticky keys file as a backup, then replace the sticky keys file in System32 with the command prompt, this will allow you to access the command prompt from the login screen. This can be done with the two following commands:
X:\Sources > copy c:\windows\system32\sethc.exe c:\
X:\Sources > copy /y c:\windows\system32\cmd.exe c:\windows\system32\sethc.exe
From here, you can exit out of the command prompt and Windows Setup to cancel the installation.
Now, in Windows 10 version 1803, a patch was released that removed accessing sticky keys from the login screen, however if you press "Forgot Password" and press the shift key five times, the sticky keys prompt will display, but because we replaced sticky keys with the command prompt, we should now be greeted with an Administrator privileged command prompt.
From here you can add an account as an administrator or change the password of an existing one. Below are the commands to both change the password and create an administrator.
To create an administrator account:
C:\Windows\System32 > net user [ new username] [new password]
C:\Windows\System32 > net localgroup administrators /add [new username]
To change the password of an existing account:
C:\Windows\System32 > net user [old username] [new password]
Hopefully the process was successful. After logging in, we now have to undo what we just did.
The best way to revert the changes is through the re-installation USB.
After you have booted the USB and gotten the command prompt again, all of the changes can be undone through the following two commands:
X:\Sources > copy /y c:\sethc.exe c:\windows\system32\sethc.exe
X:\Sources > del c:\sethc.exe
Success! Hopefully everything has worked properly, now I must add that sometimes this method does not work because sticky keys has been disabled on the installed operating system, if that is the case then this process will fail.