Is there a corresponding folder in C:\Users\...? [Check for hidden folders as well just to be on the safe side]
If not [and that's the answer I'm expecting] then that additional user account might have been created but never logged in to. That would also account for its absence from the Registry.
Both the Registry entry & the C:\Users\... folder are created the first time an account is logged into not when the account is made.
Does the response to the Command prompt command net user list the unknown account? I think it will. If so then net user commands can be used to delete that account.
- Does the shop that you bought the computer from confirm that they create user accounts when preparing computers for sale? If not then you should realise that an unauthorised individual has had access to the computer at some stage. You do not know what else they have done to it. In such circumstances, reinstalling Windows is the only way to be sure that you do not have malware planted on the computer.
- If the shop confirm that they did reset the computer before sale and created that account as part of doing this task then the account does not seem suspicious and deleting the account is merely a case of tidying things up.
[Why did they reset it? Is it second-hand?]