If you change your password at the mtnl website and next time you put on your system the net is down, don't worry. Simply go to the 192.168.1.1 interface of the ADSL and change your stored password. It is in Advanced ATM VCC . Do not forget to go to Tools > System and click 'Save and Reboot' . Now your net is up again.
I had to wait 3 disconn days before finding this out. Rony is giving it out free. Which brings me back to that eternal question ... Why is that damn password change option on the MTNL webpage if they are gonna shut you out if you don't login with their password.