Hi bobbymcgee
You mention two login screens? Not at the same time, though? .... I expect that what your friend is seeing is a single screen, with either two operating systems to choose from (which in turn produce two different login screens with different usernames for login)....OR is seeing a single screen with multiple users listed, and depending on which user is selected & logged in - the destop backgrounds are different.
I have never heard of a system that would allow two different logon screens
at the same time [not a personal PC, anyway .... in a business client-server setup, many users log into one big computer ... or, even longer ago, very large mainframes had hundreds of "terminals" which users would use to access programs].
Two operating systems showing at boot/restart
This means that your friend, whether by accident or on purpose, has two operating systems installed on the same computer. If he only wishes to use one, and get rid of the other, that is fairly easy to do. To only remove the option to start the unwanted operating system, then - when booted into the preferred operating system:
1) Right-click the Windows Start Menu icon
2) Select System
3) Select Advanced System Settings
4) In the Startup & Recovery section, select Settings
5) In the System Startup section, from the drop-down Default Operating System menu, choose the preferred system.
6) Then set the Time to Display List of Operating Systems to 0 seconds
7) Then select OK
This will cause the preferred operating system to boot without displaying the option to enter the other. [You can uninstall the other - user's choice - or just keep it hidden .... keeping the unused operating system will of course mean a bit less room on the hard drive]
Two (or more) users showing at boot/restart
If there are two or more user accounts created for the only operating system on the hard drive, of course they will show at startup, even if they don't have passwords- or are set to have the passwords entered for them automatically .... how else could a user be selected? If there should only be one user, and somehow another user is showing up -- so long as the 'extra' user isn't the "elevated Administrator" that is built into Windows 10 -- you can remove that user. Be aware that you'll have to choose whether or not to save data/documents/programs/etc... from the account that is being removed. To remove a user:
1) Right-click the Windows Start Menu icon
2) Select Control Panel
3) (make sure Control Panel is in "Large Icons" view)
4) Select User Accounts
5) Select Manage Another Account
6) Select the account you wish to remove
7) Select Delete this account
8) Choose either to Delete or Keep the accounts files.
AutoLogon
Many users prefer to have the passwords entered automatically at system startup/restart ... at home in a non-business environment, it's somewhat reasonable. To bypass the logon screens by means of an automatically entered password, there are at least three different methods.
1) A very simple one is to use the Microsoft/SysInternals utility Autologon --
Autologon
2 & 3) The other two methods are a bit technical - one uses an Advanced User Accounts setting (via netplwiz) and the other uses a Registry edit. Not recommended if your friend tends to type with wild abandon. Here's a link to instructions for those last two options --
How To Automatically Login In Windows 1
Let us know if you have any questions.
[P.S. ... Kristofferson/Joplin fan?]