Suddenly lost Administrator rights on Windows 10

Hi Sam. I'm Greg, an installation specialist and 9 year Windows MVP, here to help you.

If you have lost Admin rights on the sole acccount then try these steps leading up to if necessary creating a new Local Account which sometimes is the only way to escape Account Corruption in Windows 10:

Right click Start button to open Run box, copy and paste in netplwiz, press Enter.

Highlight your account, then click Properties, then Group Membership tab. click on Administrator, then Apply, OK, restart PC.

If that doesn't help then try this: https://www.kapilarya.com/fix-lost-administrati...

If nothing helps try creating a new Local Admin Account to sign into to see if it works: http://www.howtogeek.com/226540/how-to-create-a...

If you can't get the rights to do this then use whichever method works here to enable the hidden Built-in Administrator to be used only in emergencies:
https://www.tenforums.com/tutorials/2969-enable...
https://www.isumsoft.com/it/enable-hidden-admin...

It may be necessary to create Windows 10 Installation Media on another PC to access the Command Prompt without needing a password: http://windows.microsoft.com/en-us/windows-10/m...

Insert media, boot it by powering up PC while pressing the BIOS Boot Menu Key: https://www.sysnative.com/forums/hardware-tutor...

Choose the boot device as a UEFI device if offered. If the media won't boot you may need to enter BIOS/UEFI Setup (pressing key given in chart in link above) to turn off Fast Boot or Fast Startup first.

After it loads, on second screen, choose Repair Your Computer, then Advanced Startup Options, first try System Restore to a point before this. If that fails then choose Command Prompt to follow the step above to access Built-in Admin Account.

Sign into Hidden Admin account, see if you can use netplwiz now to elevate the account. If not try another of these methods: https://www.windowscentral.com/how-change-user-...

If not then set up a new Local Admin Account, sign into it, move your files over, set it up, hide the Hidden Admin Account, when ready delete the old account in Settings > Accounts > Family and Other Users.

I hope this helps. Feel free to ask back any questions and let us know how it goes. I will keep working with you until it's resolved.

I tried the first option & the same thing happened when I pressed enter after entering netplwiz (my PC made an error sound and it showed the same box & asked for an Admin pw, the "yes" option grayed out). With the second option on Kapilarya, when I booted into safe mode and clicked "command prompt", my PC asked me to sign into an account named Admin, but the pw I entered was incorrect or it doesn't have one anymore? Through the third option on howtogeek, in the settings "family & other users" wasn't there for me, probably because I'm not an Admin. I looked into the next link (tenforums); all of the steps required me to be logged in as Administrator. I'm not sure how to login as Administrator in general & because I don't know the pw. I haven't looked into any of the other links yet but that's where I'm at currently.

If you enable the built-in Admin account used in emergencies like this to confer Admin powers upon an account in netplwiz > Properties > Group Membership, leave it's password box blank to sign into it.

If you have a UAC box with the Yes button greyed out, see here:
https://www.tenforums.com/tutorials/108280-fix-...
https://winaero.com/blog/fix-yes-button-disable...

I gave you a method to Sign into built in Admin from the Log on Screen:
https://www.isumsoft.com/it/enable-hidden-admin...