@exo15, I have now replicated your situation and can confirm the loophole in Windows 10 you have accidentally found. I installed Windows 7, activated the built-in administrator account and removed all other user accounts. I then upgraded to Windows 10 which after the upgrade naturally had only this one user account, the built-in administrator account.
This allowed me to connect the built-in administrator account in Windows 10 to a Microsoft account and use Windows Store to download apps. Notice that because the default restrictions, this is normally not possible; when the built-in admin account is used as it should, not as a sign-in account to Windows but solely for administrative tasks it is not possible to use most of the Windows Apps with it (Store, Edge and so on), and it cannot be converted to a Microsoft Account.
The loophole you found, activating the built-in admin in previous version and then upgrading to Windows 10 using it seems to override all default security restrictions on the said built-in admin account, making it possible to connect it to a Microsoft account. However, as this is meant never to happen, once you have converted the built-in admin account to a Microsoft account, it is no longer possible to convert it back to a local account. It is absolutely impossible, that is why the Your account page does not even show the Sign in with a local account instead option:
The loophole you found is so bad that I am sure that Microsoft will fix this in the near future, making it impossible in any upgrade or install scenario to convert the built-in administrator account to a Microsoft account.
Therefore, the recommendations in my previous post are in my opinion the only valid options for you. I repeat the options here:
Windows system administrator, the built-in administrator account is not meant to be nor should it be used as a normal Windows sign-in account.
By default the built-in admin account can't use Store, Edge and most of the so called Store Apps. If you have made the very bad decision to use the built-in administrator account as your sole user account in previous versions of Windows, you need to be sure it is not active when you upgrade. Create a local admin account for yourself, sign in to that account and disable the built-in administrator account before upgrading to Windows 10.
If you stubbornly insist "knowing it all" and continue using the built-in administrator account as your Windows sign in user account and upgrade to Windows 10, be sure not to repeat this thread's OP's mistake to convert it to a Microsoft account!
There are valid reasons why the built-in administrator account in Windows has extra security measures, why it is not possible to use Store Apps with it, why it is not possible to convert it to a Microsoft account when installation or upgrade is done correctly, using a normal local user account instead.
@Night Hawk, I don't know where to start with you! Sometimes this really is difficult! Let's try:
Night Hawk said:
The OP's issue is exactly that, he has accidentally found a loophole to convert the built-in administrator account to a Microsoft account, which usually is not even possible. Read my reply to OP at the beginning of this post.
Night Hawk said:
The accounts shown in Your account page under the title Other accounts you use are not Windows user accounts. In fact they have absolutely nothing to do with Windows user accounts. They are the other MS accounts you have added to the Mail, Calendar and / or People apps, other accounts that you use with those apps when signed in to your Windows 10 user account. The page shows on top your Windows user account and underneath those other MS accounts of yours you have added to the Mail, Calendar and / or People apps, or which you'd like to add to the Mail and People apps.
Try it. Adding an account in Your account > Other accounts you use does not add that account as a user account in Windows 10. If you sign to Windows 10 using your MS account, then go to Mail app and add another of your MS accounts, this another MS account will now be listed under the title Other accounts you use in the Your accounts page, but it will not be added as a user account to your Windows 10.
The same works the other way around, too; you can add your other MS accounts in Your account page and then when you want to add new accounts in mail app you don't have to go through the Mail setup process for those accounts because Windows already knows those accounts are yours and when you use the Add account option in Mail app, those accounts are already listed and will be added with one click:
Please try to understand the difference between Your account > Other accounts you use and Family & other users > Add someone else to this PC. The first one adds additional MS accounts to your Windows 10 user account to be used with Mail, Calendar and People apps, the second one adds new user accounts to your PC.
Night Hawk said:
As has already been explained, the OP has accidentally managed to do something which should be impossible, and is impossible when Windows is installed, upgraded and used correctly: the OP has managed to upgrade Windows 7 to Windows 10 using the built-in administrator account as the user account and convert it to a Microsoft account.
Night Hawk said:
Repair install does not change or reset the user account types. AS the OP's native built-in administrator account is now a Microsoft account, no repair install or system file check will revert it to a local account again, nor will the option to use a local account be shown whatever the OP does. The only options are those three I have now posted three times, continuing to use the computer with the built-in admin accidentally converted to a Microsoft account is not a viable option.