Website not reachable for some reason

Check and/or restart is your Web server running. To do so, you need to connect to server over SSH first.

For Apache:

sudo systemctl status apache2
sudo systemctl restart apache2

For Nginx:

sudo systemctl status nginx
sudo systemctl restart nginx

Try to access via browser again. If it doesn’t work try another browser or clearing cache just in case. But if it helped, we will try debugging it and make it doesn’t happen again. If nothing helps, check logs. For Apache you should have two logs and you can open them with any text editor:

sudo nano /var/log/apache2/access.log
sudo nano /var/log/apache2/error.log

For Nginx look for logs in following directory :

/var/log/nginx

If I recall correctly, there should be access_log and error_log. If you need help analyzing logs, feel free to ask.

Note: Make sure you didn’t enable any firewall in meanwhile. If it stopped working from it self, this is not case, but just to note. =)