/bin/bash: Permission denied

[root@host /]# su - user1

/bin/bash: Permission denied

Scenario:  My system is not responsive to any process, so i was forced to reboot. Suddenly i cannot login as ordinary user  "user1" 

Solution:  I look the permission of /bin/bash

[root@host ~]$ ls -l /bin/bash

-rwx------. 1 root root 938736 May 10  2012 /bin/bash

tried to change the permission 

[root@host ~]$ chmod 700 /bin/bash

-rwxr-xr-x. 1 root root 938736 May 10  2012 /bin/bash

Then I try to change the permission of the whole /bin  directory

[root@host ~]$ chmod -R 755 /bin

NOW I  CAN login...