Nothing responds. Working out why.
FIRST, ESTABLISH SCOPE
Can you ping the address? A reply means the machine is up and the network works, so the problem is a service. Can you reach SSH? If yes, the machine is fine and you can diagnose from inside. Can you reach the site but not SSH, or the reverse? That narrows it to one service or one firewall rule.
IF NOTHING RESPONDS AT ALL
Use the provider console, which connects to the machine directly rather than over the network. That distinguishes a network problem from a machine that is not running.
If the console shows the machine running but unreachable, suspect the firewall or the network configuration. If the machine is not running, start it and check why it stopped.
IF YOU CAN REACH THE CONSOLE
Check disk space first. A full disk causes services to fail in ways that look like anything else. Check memory and whether the kernel has been killing processes. Check service status. Read the system log around the time it stopped.
IF IT IS ONLY YOU
Test from another network. Your address may be blocked.
