cannot log in via console, cannot su(1), only as root

[martinko]

martinko wrote:
> hello list,
> 
> i was updating sw configuration of my old computer and towards the end i 
> noticed i couldn't log in on local console other than root.  i tried 
> remote ssh using public keys which worked but i found out su(1) to any 
> user except root does not work either.  i've no idea how i could 
> possibly manage to "break" my system like this and unfortunately i need 
> to fix it by tomorrow.  therefore i would really appreciate your prompt 
> hints as what to check etc.
> 

some more details follow ...

upgrade from 6.0-R to 6.2-R
everything went ok ..
i was doing changes in /etc based on my other computer settings
i was working via ssh(1), therefore i haven't noticed when logging on 
console stopped working.

what works:
log in via ssh(1) using public/private keys
log in on local console as root
su(1) to root

what doesn't work:
log in via ssh(1) using password
log in on local console as a normal user
su(1) to a normal user (it even doesn't ask for password a throws "sorry")

besides, as root i'm able to change passwords via passwd(1), but it 
doesn't help and a normal user cannot change their own password (old 
password check would fail).

i ran vipw(8) and it doesn't seem to me there's something wrong with my 
files.

any hints pls ??

m.