It seems you have changed the port level access settings of your default port. go to IS admin page —> security —> ports. Look for your default port and go to access mode for that port, click on edit and see if it is set as ‘Deny By Default’. If this is the case then choose ‘Allow By Default’ and then restart your server using default port and then try accessing IS admin page and developer.
By default installed server in 6666 port, when I started IS, I couldn’t open in developer and in explorer, So changed the port when I started using command prompt. Now I able to open thru developer and explorer.
As you said I verified all the three ports access settigns they are in “Allow By Default” state.
9999 - Diagnostic port
6666 - Default port
8888 - New port (now made it as default port).
Try netstat -an and check if port 6666 is listening or not, both while your IS is running and shutdown. This might give some clue, if it is in listening state both times or not in listening state both times.
If it is listening both times, some other program is using that port (in which case IS should throw error saying could not bind to that port).