How come it won't let my uncle sign in to facebook on my laptop?

[Nervana]

It must be because one of these reasons:

1- You were given a wrong password.
2- You used CAPS lock the wrong way while entering.
3- There's a temporary error with his profile. It should be fixed in a couple of hours automatically.
4- It's hacked.

You can report the hacking (if that's the case) using another facebook account [Log in, open the Help Center then click a link on the right hand-side that says "is your profile hacked?" or something of that sort).

I hope I helped.