Help needed

I recently purchased TP-LINK TL-WR740N wireless router. I installed it correctly and had no problem whatsoever. I used the easy startup guide in the cd provided. It asked me my bsnl adsl connection username and password and after finishing the process it connected to the internet automatically. Then i went to tp links website and downloaded the latest firmware after which the router rebooted. Now my internet was disconnected. I chose my usual dial up and entered my username and password. But now the internet is not connecting (the modem has reported an error) Please help.
Please post the exact error message that you are getting.
Also, try the setup guide again.
PS: The wise have always maintained, don't upgrade firmware unless necessary.