I can't connect - "connection refused" or "connection timed out"

Work through these in order: confirm the instance is Running; use the current public IP from the console (it can change after a rebuild); test from a different network; double-check your key and username; make sure a firewall isn't blocking port 22; then restart the instance. If SSH worked before and suddenly stopped, or only one of several instances is affected, contact support with the instance ID - it may be on our side.