Unable to block a website through System32/drivers/etc/hosts

Try removing the www. Just:

127.0.0.1 thatstamil.com
127.0.0.1 tamil.oneindia.com
127.0.0.1 facebook.com

If you put in www.thatstamil.com, but are accessing thatstamil.com, the latter is not the same fully qualified domain name (fqdn) as www.thatstamil.com. Try using the following:

127.0.0.1 www.thatstamil.com
127.0.0.1 thatstamil.com

Try to block tamil.oneindia.com instead of thatstamil.