Windows 10: How to remove an Unknown Account that has Special permissions

I really hope this can be fixed because it's stressful knowing there is someone who has full access to my computer and I'm unable to remove them due to it, despite being an administrator whenever I try to it says 'Access Denied' so I'm unsure on how to remove them, for the record I'm the only one that should be using the laptop at home. The internet didn't yeild any solutions so I came here, is there a way to remove their access while they have the most permissions on my laptop?? Or is my laptop unable to be recovered for good, I really don't want to have to purchase a brand new one but if it'

:)

 

Unknown account removal

In a 'permissions' dialog an attempt to remove an UNKNOWN ACCOUNT prompts that inheritance first must be disabled. Two options are offered...

1) Convert inherited permissions to explicit permissions on this object
2) Remove all inherited permissions from the object

Which should be chosen, and will other accounts be affected? Or, would it be prudent to ignore the unknown account?

This is an "Sxxx" account and does not appear in the USERS account list, nor with other normal registry accounts.

 

Account Unknown has full Security permissions on my own User - huh?

Hello glnz,

You will see "Account Unknown" for an account that is not currently available. This could be from an account you deleted that had permissions, or from an account on another computer that is not connected.

Either way, it's safe to remove any listed "Account Unknown" entries in permissions if you are sure it's for an account that will no longer need permissions for the item.

 

Remove account

I suggest you backup your personalized files first before removing the account.
To delete an account, follow these steps:

1. Press WIN + X keys and click Command Prompt (Admin) from the menu.
2. Type the following command and press Enter. Replace test with the name of your sister's account. Code: