No command line prompt for root

[LUK ShunTim <cestluk@polyu.edu.hk>]

Hi,

Something strange happened to my Debian system. I can login as an
ordinary user and it works normally but when I login as root, it printed
out the motd on the screen and said that root has been logged in. A
'who' from another user confirms it. It even told me "no mail for root"
but I don't get the command line prompt # and so I can do nothing as
root. Su'ing from an ordinary user meets with the same failure. A Ctrl-C
will give back the login: prompt. I've used the rescue disk to boot up
and checked the .bash_profile, .bashrc and /etc/passwd files and they
are all OK. 
(I upgraded to slink, kernel 2.0.35 from hamm a few days ago.)

Any ideas as to what happened and what is the remedy will be very much
appreciated. 

ST