How to confirm that the client program is working normally?

Press hotkey Ctrl+Alt+r in OS, the password checking box will appear
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Client can not be found by Server?

First, please make sure that the server has fixed IP address.
Second, make sure that the client program is working normally and it has correct server IP address.
Third, make sure that the network link between server and client is no problem.
Fouth, make sure that the firewalls of the server and the client are off.