You can confirm with local resellers or call the number directly. http://www.tp-link.in/where-to-buy/resellers.aspx Sales phone: +91 9768012285 (10:00AM to 6:00PM, Monday to Saturday. Excluding...

Your device is old. Few people still use it. I even cannot find its user guide anymore. My only suggestion is to reset it to factory defaults.

Why not reset it to factory defaults?

Devices connected to the range extender can obtain IP address assigned by the MTS device? Can you provide screenshots of status page and system log?

Firmware of your WR841N is up to date? Check the link speed on your laptop. Try to test the speed by some other clients and make a comparison.

Install the adapter on other computers or buy other adapters which will work on this computer.