cannot start apache

[rippon]

Cannot start Apache. I get this:

12:40:29 [main] Initializing Control Panel
12:40:29 [main] Windows Version: Windows 8.1 Pro 64-bit
12:40:29 [main] XAMPP Version: 5.6.19
12:40:29 [main] Control Panel Version: 3.2.2 [ Compiled: Nov 12th 2015 ]
12:40:29 [main] You are not running with administrator rights! This will work for
12:40:29 [main] most application stuff but whenever you do something with services
12:40:29 [main] there will be a security dialogue or things will break! So think
12:40:29 [main] about running this application with administrator rights!
12:40:29 [main] XAMPP Installation Directory: "c:\xampp\"
12:40:29 [main] Checking for prerequisites
12:40:29 [main] All prerequisites found
12:40:29 [main] Initializing Modules
12:40:29 [Apache] Problem detected!
12:40:29 [Apache] Port 80 in use by "Unable to open process" with PID 4!
12:40:29 [Apache] Apache WILL NOT start without the configured ports free!
12:40:29 [Apache] You need to uninstall/disable/reconfigure the blocking application
12:40:29 [Apache] or reconfigure Apache and the Control Panel to listen on a different port
12:40:29 [main] The FileZilla module is disabled
12:40:29 [main] The Mercury module is disabled
12:40:29 [main] The Tomcat module is disabled
12:40:29 [main] Starting Check-Timer
12:40:29 [main] Control Panel Ready
12:41:41 [Apache] Problem detected!
12:41:41 [Apache] Port 80 in use by "Unable to open process" with PID 4!
12:41:41 [Apache] Apache WILL NOT start without the configured ports free!
12:41:41 [Apache] You need to uninstall/disable/reconfigure the blocking application
12:41:41 [Apache] or reconfigure Apache and the Control Panel to listen on a different port
12:41:41 [Apache] Attempting to start Apache app...
12:41:41 [Apache] Status change detected: running
12:41:42 [Apache] Status change detected: stopped
12:41:42 [Apache] Error: Apache shutdown unexpectedly.
12:41:42 [Apache] This may be due to a blocked port, missing dependencies,
12:41:42 [Apache] improper privileges, a crash, or a shutdown by another method.
12:41:42 [Apache] Press the Logs button to view error logs and check
12:41:42 [Apache] the Windows Event Viewer for more clues
12:41:42 [Apache] If you need more help, copy and post this
12:41:42 [Apache] entire log window on the forums

What should I do? (brand new to all this)
Please help.
Thanks.