I had the same issue and none of the answers solved the problem.
I ran:
sudo nginx -t
to test the config file at /etc/nginx/sites-available/default.
It gave me these errors:
nginx: [emerg] unexpected end of file, expecting "}" in /etc/nginx/sites-enabled/default:115
nginx: configuration file /etc/nginx/nginx.conf test failed
So I went into the config file and on the last line there was
#}
I uncommented, ran the test command again and it worked