None of these worked for me. I had to go to a SuperUser question.
If it is a System Process—PID 4—you need to disable the HTTP.sys driver which is started on demand by another service, such as Windows Remote Management or Print Spooler on Windows 7 or 2008.
There is two ways to disable it but the first one is safer:
Go to device manager, select “show hidden devices” from menu/view, go to “Non-Plug and Play Driver”/HTTP, double click it to disable it (or set it to manual, some services depended on it).
Reboot and use
netstat -nao | find ":80"
to check if 80 is still used.
This is the one that worked for me!