Hi James
My name is Andre Da Costa; an Independent Consultant, Windows Insider MVP and Windows & Devices for IT MVP. I'm here to help you with your problem.
Give it 3 hours then try using the new password again - make sure the computer remains connected to the Internet. Sometimes it takes some time for the password reset to federate. If it doesn't work try using the old password.
Try restarting a few times then try again.
Try disconnecting from the Internet and try again.
If that does not work, reboot in Safe Mode then try signing in.
At the sign in screen:
Hold down the shift key on your keyboard while clicking the Power button on the screen.
Continue to hold down the shift key while clicking Restart.
Continue to hold down the shift key until the Advanced Recovery Options menu appears.
Click Troubleshoot
Click Advanced options
Click Startup Settings
Click Restart
Press (4) to Enable Safe Mode
Wait while Windows 10 starts in safe mode.
Log in
If you are still unable to log in, see the following:
http://answers.microsoft.com/en-us/windows/wiki...
Other things you can try - enable to built in Administrator account:
Hold down the shift key on your keyboard while clicking the Power button on the screen.
Continue to hold down the shift key while clicking Restart.
Continue to hold down the shift key until the Advanced Recovery Options menu appears.
Click Troubleshoot
Click Advanced options
Click Command Prompt
At the command prompt, type:
net user administrator /active:yes
Hit Enter
Close command prompt, restart, then try signing into the Administrator account.
Try signing in again.
Hold down the shift key on your keyboard while clicking the Power button on the screen.
Continue to hold down the shift key while clicking Restart.
Continue to hold down the shift key until the Advanced Recovery Options menu appears.
Click Troubleshoot
Click Advanced options
Click Startup repair the follow the on screen instructions.
When complete, restart.
Try signing in again.
Change password
Open Control Panel - see how to find control panel:
https://www.groovypost.com/howto/open-control-p...
Open User Accounts
Click Manage another account
Select the other account
CLick Change the password
Enter the password
Confirm the new password
Type a hint
Click Change password
or
Open Start, type: CMD
Right click CMD
Click Run as administrator
Type: net user
Hit Enter
This should reveal your account name
Type: net user YOURACCOUNTNAME *
Hit Enter
Type a new password for the account then hit Enter.
If none of the above works, you are best off reinstalling Windows 10.
How to: Perform a clean install of Windows 10
http://answers.microsoft.com/en-us/insider/wiki...
If there are files on the drive you want to recover, see - How to: Perform a Custom install of Windows 10
http://answers.microsoft.com/en-us/insider/wiki...
Step 4: how to recover your files from Windows.old:
https://answers.microsoft.com/en-us/windows/for...