Open the command prompt in administrative mode and run:
netstat -np TCP | find ":80"
The IPs on the left are your local IP. The above command will return tens or hundreds of results if you are browsing or with something connected to the internet.
A quick way to filter and get the point is to put your IP in the command
Example, if your IP is 192.168.1.10
netstat -abnop TCP | find "192.168.1.10:80"
This will return empty if there is nothing.
If you have something, it will return:
TCP 192.xx 192.xx ESTABLISHED 4444
The last number is the PID of the process in question.
To find out the name of the process:
tasklist /fi "pid eq 4444"
Return:
Image Name PID Session Name Session# Mem Usage
processo.exe 4444 nome_sessao 2 10k
So you get the name of the program that is occupying the port you want, in this case port 80.
Two programs can not occupy the same port.
If you want Apache on this port that is in use, you should either stop the other program or switch it to another port.
Note: Your question still seems confusing because the error message for when the port is in use is different from the message that is in the question.
The message is usually related to the read and write permission of a particular physical location.