1) Run the command prompt by Click the windows start menu and input "cmd" in searching box

2) Type <netstat -ano|findstr "XXXXXX">

PS : *1 the angle brakets is not necessary.

       *2 XXXX means the port number you want to check

3) if there is no message that means the port haven't been used

    if it pop-up somemessage as below, that means the port is busy.

4) type <tasklist|findstr "XXXX"> to check which program is using the port