@Abhinay
Hello, can you please help confirm some details then we will try to work it out?
1. How is the WR845N connected to the BSNL modem, is WR845N's WAN port connected to the modem's LAN port? What is its working mode? Please login to the web interface of the WR845N, then take a screenshot of the Advanced-Status page, ensure there is a correct WAN IP address.
2. If it is a standard router mode, try to change the WAN DNS server on the WR845N to Google's 8.8.8.8 and 8.8.4.4, then reboot both the modem and the WR845N to confirm again if the internet LED will become green.
3. If this doesn't help, please connect your computer directly to the BSNL modem, confirm what is the IP address, gateway, as well as the DNS server you get on the computer, ensure the internet is working fine.
Thanks a lot~