There is something using port 80.
Click on the Netstat button in the XCPv3 and see if it has more details about what the SYSTEM is.
Usually it is related to IIS the Windows default server which can be disabled as it uses port 80 and port 443 by default which Apache needs exclusively.
Because this issue has been covered here many times before I did a an advanced form search for post I have made for port 80 system
in the XAMPP for Windows
forum and came up with these results
, see if any have the solution for you - you will see unrelated posts that you can skip and some that relate to Vista that may also be relevant for Win7.
After reading the results above please let me know if you find a solution.