Connecting to localhost... The connection to the host cannot be opened. In port 1433, the connection fails.

When the server is started, it basically does everything, but it cannot achieve the desired results!
In DoS: Telnet localhost 1433 n times: connecting to localhost... the connection to the host cannot be opened. In port 1433: connection failed!

Finally, I found the true meaning of the problem in csdn:

Confirm SP4 () Are you sure you want to install it? The download is actually a decompression process,
After the three files are extracted to a directory, an installation file is generated !!

Miscellaneous:

1. The current database port is incorrect (usually seldom appears !)
SQL can see the TCP/IP Port in two places, one is in [Program]-> [Microsoft SQL Server]-> [client network utility], the default port is 1433, however, this is a client. It does not mean that the port number on your server is also 1433! Open [Program]-> [Microsoft SQL Server]-> [Enterprise Manager], and under the SQL server group, select your SQL Server (for example, my server: baby/bbsql (Windows NT), view its properties, which contains a [network configuration], select TCP/IP in the network configuration, view its properties, if it is 1433, it is correct, otherwise, the configuration is successful!

2. Disable the firewall, including anti-virus software monitoring settings. Also, check whether dynamic ports are configured. Use netstat-a to check which program occupies the port.

In addition, SQL server startup:

Start the service program in the Service Group
C:/progra ~ 1/mi6841 ~ 1/MSSQL/binn/sqlagent.exe
The SQLServerAgent service cannot be started on the local computer.
Error 1086: the dependent service or group cannot be started.

Cause: MSSQLServer is not started!
C:/progra ~ 1/mi6841 ~ 1/MSSQL/binn/sqlservr.exe