messed up user accounts

You renamed an account that had the username Administrator?

That's the normally disabled Built-In Admin account.
Built-In Administrator account - Enable or Disable - TenForumsTutorials
But I don't think you will be able to enable it in your current state.

In the tutorial linked to below, you will get the chance to use the Built-In Admin account [even though you cannot currently enable it yourself] to create an Admin account of your own then disable the Built-In Admin account when you have finished. The Built-In Admin account has had various undocumented limitations that have varied between Windows 10 Versions and it is really only intended for this single purpose [creating an Admin account of your own].

This procedure will take you through the whole thing. It was written for your situation - its name merely reflects the symptom that most people first report.
Fix UAC prompt has greyed out or missing Yes button - TenForumsTutorials

If you have any questions along the way then just post them here.

---

Since you bought it from eBay, you might be better off just doing a clean install of Windows.
Clean Install - TenForumsTutorials

If I was going to do a clean install, I would backup all the existing drivers beforehand.
Backup and Restore Device Drivers - TenForumsTutorials

If I was going to do a clean install, I would also check my activation first. If it is 'activated with a digital licence' then it will self-activate after the clean install [when you first go online] without any other action being needed.
Settings, Update, Activation



By the way, the username User often indicates that it was originally set up by the shop that sold it rather than by the purchaser.

Denis

You'll see in that tutorial that I am rather biased towards local accounts and I suggest that you make the "main user account" a local one. If you will have a need for an MSAccount then you can always add that afterwards.

Windows can be awkward about creating a local account during a clean install but can be made to allow this by simply not connecting to the internet during that clean install.

Denis

Hello @bjproc,

bjproc said:

It's a fujitsu esprimo e3521 and I just can't get it to boot from the usb with the clean install of win10.

I click F12 on start up, pick the USB to boot from and it just sticks on a black screen and the small white cursor flashing on the top left ????

[1] Where did you get the ISO from to create the installation media?
[2] What did you use to create the installation media?
[3] Did you disable Fast Boot first [ if enabled ]? . . .

> How to Turn On or Off Fast Startup in Windows 10

I hope this helps.

bjproc said:

Downloaded through MS with their media creation tool for USB stick.

- - - Updated - - -

Oh, its just started, maybe it was just slow.

Thank you again for the help.

You are VERY welcome.