Problem setting up xampp server on windows 7

Having this error after installing xampp
9:02:10 AM [mysql] Attempting to start MySQL service...
9:02:13 AM [filezilla] Attempting to start FileZilla service...
9:21:07 AM [Apache] Problem detected!
9:21:07 AM [Apache] Port 80 in use by "Unable to open process" with PID 4!
9:21:07 AM [Apache] Apache WILL NOT start without the configured ports free!
9:21:07 AM [Apache] You need to uninstall/disable/reconfigure the blocking application
9:21:07 AM [Apache] or reconfigure Apache and the Control Panel to listen on a different port
9:21:07 AM [Apache] Attempting to start Apache service...
what am i doing wrong?