change it's value to 0 (from the current 1) and click OK. Select it in the left pane and, in the right pane, double-click the DWORD ExcludeFromCPL. Navigate to HKEY_CURRENT_USER\AppEvents\EventLabels. Hit Win+R and type regedit, then hit Enter. Here's how to add them back - via a registry hack - to the program events list under CP > Sounds for easy customization.
You'll notice though that in Windows 8 and 8.1 some program events don't show up there at all, including the logon, logoff, shutdown ones. Alternatively you can open the RUN prompt by pressing Win+R and typing MMSYS.CPL then click the Sounds tab. In order to change the sounds Windows uses, you would usually go to Right-click Start > Control Panel > Hardware and Sound > Change system sounds under Sound.
