Disconnect from the server & then restart Invision .. you might have been disconnected from the server & lost your settings. If that didnt fix the sound events, continue onto troubleshooting.
 Sound FX troubleshooting:
Invision settings:
1. check that you're scheme (theme) points to the correct path for the sound fx folder
2. check that you've ticked the checkboxes 
Enable Sound FX and 
Hear own sounds in the sound manager.
If you made any changes, dont forget to Save All Settings
mIRC settings:
File -- Options -- Sounds may have to tick the checkboxes  
Enable Sounds and in the Sounds sub menu 
Requests .. 
Accept sound events
Hope that helps you out 
 
Hugz
Dana
xXx