Can't reach the controller

Four things, in this order: same network, right address, port open, firewall allowed. Almost every “device offline” is the first one.

1. Same network

The PC and the controller must be on the same subnet. A machine on 192.168.1.x cannot be reached from a PC on 192.168.0.x or from a phone hotspot. Check the PC's address with ipconfig and compare the first three groups.

2. Right address and port

Confirm the IP shown on the machine against the one entered in Net Center. A single wrong digit is the second most common cause — and it looks exactly like a dead machine.

3. Reachable at all

ping <machine-ip> from a command prompt. No reply means cabling, switch or address — not the software.
If ping works, check the port: telnet <ip> 8080 (or use Net Center's device list).
Watch the link indicator on the board while doing this. It should react when a connection attempt arrives.

4. Firewall and antivirus

Windows Firewall blocks inbound by default on public networks. If the PC switched itself to a “Public” profile after a Windows update, an otherwise correct setup stops working overnight. Set the network to Private and allow Net Center.

One device at a timeIf two PCs try to control the same machine with the same session, one of them will appear permanently offline. Close the other instance first.

If nothing helps

Send us: the machine's IP and port, the PC's IP, the output of ping, and whether the machine shows up in Net Center at all. “Not in the list” and “in the list but offline” point at different layers.