Port 80 is occupied by Windows. Google "disable IIS"
While your at it, if you have skype, you can click on Tools menu and select Options. Click on the Advanced tab, and go to the Connection sub-tab. Untick or uncheck the checkbox for Use port 80 and 443 as an alternative for additional incoming connections option. Click on the Save button and then restart Skype to make the change effective.
That way neither windows IIS service or skype will argue with your apache server for port 80.
