I run Plone on port 80 for our intranet server.

Once in a while, port 80 gets hijacked by some services, Which is suspected to be our ERP Microsoft Nav MSSQL services related.

To restore order, i follow these steps

1. Reboot the machine
2. Open command prompt using … start > Run > CMD
3. Type the command “netstat -ano”
4. Note the Process ID PID that is using the port by analyzing the results.
5. Use taskkill /pid# to kill that process

Now, restart Plone, or Apache, or whichever server you are using