1. In the Registry, for each user these sound definitions are at
[tt]HKEY_CURRENT_USER\AppEvents\Schemes\Apps\.Default[/tt]
Under each of the keys listed are two sub-keys: [tt].Current[/tt] and [tt].Default[/tt]
For [tt]SystemStart[/tt] I have [the above...]
[tt](Default) REG_SZ (value not set) [/tt]
and under [tt]SystemStart\.Current[/tt] is
[tt](Default) REG_EXPAND_SZ %SystemRoot%\media\Windows XP Startup.wav[/tt]
For [tt]SystemExit[/tt], the path is the same, except that the file is [tt]Windows XP Shutdown.wav[/tt].
In each case the [tt]\.Default[/tt] values are the same.
Also, the default established when a new user is defined is located at
[tt]HKEY_USERS\.DEFAULT\AppEvents[/tt]\etc.-as-above
(Windows has a lot of 'defaults', doesn't it? Gotta keep 'em straight.)
(I have Windows XP Pro - SP2, but I don't think that there should be any differences.)
2.
Somtimes one can reset an error condition by turning off the setting, then turning it on again. So (and there is no guarantee on this; and this process may be overkill):
In the Control Panel / Sounds that you reference -
a. Set the Sound value to "[None]"
b. Logoff the user (or do a Shutdown if desired)
c. Logon again
d. Re-establish the desired .wav sound. Test.
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.11) Gecko/20071127 Firefox/2.0.0.11