A, first of all, please check the firewall settings, it is recommended to temporarily close the firewall;

B, it may be caused by the adjustment of QQ system, so some segments can't log in. I suggest you try again later.

C. Try to use selective login server (there are currently three modes, namely UDP mode, TCP mode and member VIP mode).

Operation method: Set the advanced settings in the lower left corner of the login window-select the login server, and then select UDP mode, TCP mode, and member VIP mode (members only);

D, it may be that the agent you used has expired, so you can log in normally with a new agent or without an agent.

Operation method: In the lower left corner of the login window, set Advanced Settings-Network Settings-Type, and choose not to use proxy, or other modes (please test whether it can be used normally after selecting proxy);

E, because the LAN is blocked (the port is blocked), your QQ can't log in.

Solution: Try using an HTTP proxy.

Operation method: In the lower left corner of the login window, select Advanced Settings-Network Settings-Type, and select HTTP proxy (after selecting proxy, please test whether it can be used normally);