Did he look in the left hand corner to see if there are any additional user accounts to sign into? See the following:
Troubleshooting log in issues in Windows 10 – Incorrect Password Errors
http://answers.microsoft.com/en-us/windows/wiki...
Also try the following:
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
