I'm assuming he's forgotten his old password - in which case your guidance won't work.
But that brings up one other possibility...
DG: have you made very certain that your laptop's NUM LOCK and CAPS LOCK keys weren't hit? I know that sounds like a dumb mistake, but I've made it. More than once, tbh.
If you haven't yet powered off the laptop, do so. Wait a couple of minutes and then try reboot and try the old password one more time.
ALSO, does your system provide a password hint? It will only help you if you changed the password and forgot that you'd done so. But see what the hint is. It might just jog one of your brain cells loose.