For this scenario, I would perform the following checks:
* Check if any firewall is blocking port 9090
* Check if the port number 9090 is not used by another application. If any, then I would kill that process and try to start all servers again.
Also, I would check for errors in the log files of the Virtual DataPort server and the Web Design Studio located in the ***<DENODOHOME>/logs*** folder.
You can have a look at the Knowledge Base article [Ports needed by the VDP Server](https://community.denodo.com/kb/en/view/document/Ports%20needed%20by%20the%20VDP%20Server) for more information.
Hope this helps!