No SSH and GUI access on Proxmox usually means the network stack or the web service died. Fix it from the console by checking the interface, restarting pveproxy and pvedaemon, and making sure /etc/pve is mounted.

Check the network first
Log in at the physical console or via IPMI. Run ip a and confirm the bridge has an IP. If not, bring it up manually:
ip link set vmbr0 up
ip addr add 192.168.1.100/24 dev vmbr0
ip route add default via 192.168.1.1
If SSH is still down, check the service: systemctl status ssh. A common culprit is a bad /etc/network/interfaces change. Validate the config before rebooting — see Proxmox configuration validation.
Restart the web services
The GUI runs on pveproxy and pvedaemon. Restart both:
systemctl restart pvedaemon pveproxy
Check they’re listening: ss -tlnp | grep -E '8006|22'. If pveproxy fails, look at journalctl -u pveproxy. Sometimes the service hangs after a package update.

Verify /etc/pve is mounted
Proxmox stores cluster config in a FUSE filesystem at /etc/pve. If it’s not mounted, the GUI and CLI tools break. Check with mount | grep pve. Remount it:
pmxcfs -l
If that fails, the cluster filesystem may be corrupted. Restore from backup or check Proxmox backup server host restore for recovery steps.
What I’d do
Start with the network — it’s the most likely and easiest to fix. Then restart the web services. Only dig into pmxcfs if those fail. This is a homelab, not an enterprise; don’t overthink it.