Your computer could not connect to another console session on the remote computer because you already have a console session in progress.

You can use port tester to verify if computer you are connecting has Remote desctop service available.
1.Download porttester unzip and run (no installation required).
2.Specify computer name and port 3389 (RDP port)
If it will return "Port unavailable" that means there is no physical connection to remote
desktop service on target computer.

what is port ?

< Imagine server like big socket board and every physical socket has number. So port is just a number of this socket.
Historically major part of standard services working on predefined ports like:

http:80

https:443

So in order to check if server has service running it's good enough to check if port is accessible.

yahoo messenger port number

There are different yahoo servers (server farm ?) but there are using same port 5050:
cs215p4.msg.sp1.yahoo.com:5050
cs216p2.msg.sp1.yahoo.com:5050
cs214.msg.sp1.yahoo.com:5050

check if sql server is running

To check if SQL server is available for your computer,
you can use port-tester and check connection to port 1433.
If it's returning port available that means sql server is up and running