I Can’t start Apache after installing Xampp

[curtnorval]

That's the error Message I received:
08:17:39 [Apache] Error: Apache shutdown unexpectedly.
08:17:39 [Apache] This may be due to a blocked port, missing dependencies,
08:17:39 [Apache] improper privileges, a crash, or a shutdown by another method.
08:17:39 [Apache] Press the Logs button to view error logs and check
08:17:39 [Apache] the Windows Event Viewer for more clues
08:17:39 [Apache] If you need more help, copy and post this
08:17:39 [Apache] entire log window on the forums

and also:

08:17:37 [Apache] Problem detected!
08:17:37 [Apache] Port 80 in use by "Unable to open process" with PID 4!
08:17:37 [Apache] Apache WILL NOT start without the configured ports free!
08:17:37 [Apache] You need to uninstall/disable/reconfigure the blocking application
08:17:37 [Apache] or reconfigure Apache and the Control Panel to listen on a different port

Could someone help me? thanx