There can be a number of different reasons for why you are unable to connect to an UOX3 shard. Here are some of the most common ones:
You're trying to connect to UOX3 using an encrypted UO client
Make sure you remove/patch away the UO client encryption through Razor/UORice/similar programs before trying to connect to an UOX3 shard. UOX3 will only accept clients with no encryption.
You set the IP and/or Port incorrectly in UOX.INI
Having the wrong IP or Port in UOX.INI will give you a connection-error when you try to select the UOX3 shard in your client's server-list. The initial connection that checks for user-name/password might still go through, but not the server-selection part.
You set the IP and/or Port incorrectly in Razor/other tool used to start the client
If you set the wrong IP to connect to in Razor/other tool you use to start the client with (for some tools this means editing login.cfg in the client folder directly), you will not be able to connect to the UOX3 shard at all, it will just give a connection-error immediately. If you set the correct IP but the wrong Port, you will be able to connect and verify your user-name/password, but will not be able to connect to the chosen server in the client's server-list.
- However, if you're able to connect to the shard but get stuck on "Loading Shard" screen, it could suggest that you are trying to connect to your shard's public WAN IP from a client on your local computer/LAN. This won't work. Connect to your local IP and/or LAN IP instead, in this case. Only clients connecting from external sources can connect to your public WAN IP.
The computer you're running the UO client on might be blocking outgoing connections, either through firewalls (like the built-in Windows firewall, or ZoneAlarm) or through 3rd-party security/antivirus-software. Try to disable whichever software might be blocking the outgoing connection temporarily to see if the connection is then allowed to go through, and/or include the UO client-executable and/or outgoing IP/Port in the exclusion-rules for these softwares.
The UOX3 shard computer's firewall is blocking incoming connections
The computer that's running the UOX3 software might be blocking incoming connections, either through software firewalls (like the built-in Windows firewall, or ZoneAlarm) or through 3rd-party security/antivirus-software. Try to disable whichever software might be blocking the incoming connection temporarily to see if the connection is then allowed to go through, and/or include the UOX3 software and/or incoming IP/Port in the exclusion-rules for these softwares.
The UOX3 shard computer's router is not setup to forward incoming connections properly
If you're trying to connect to the UOX3 shard from an external computer through the Internet, you might have to setup the UOX3 shard computer's internet-router (if one is present) to forward incoming connections on the specified UOX3 port, to the internal LAN/local-IP of the UOX3 shard computer.