I will check if there is any firewall and check ports if they are open

Process of elimination, See if any other apps using the database are down. Try to establish if it's a database server issue. If not I'd move to the firewall and establish port 1521 was open on the database server. If that checked out I would start on the webserver and probably start with rebooting the webserver, since it's down anyway. Start with the simple stuff and work my way through troubleshooting the webserver, is the webserver running, services started, error logs, etc...