I recently acuired a secondhand NUC8I5BEH and installed proxmox on it. But it randomly is unreachable from my LAN. There are no errors in syslog. When I connect a monitor there is no signal. So the NUC seems crashed. The fan is spinning and the LAN lights are on. It’s not viewable on my unifi controller and it’s not pingable. Where can I start looking for the problem?