...let's begin with the obvious.
Open the Control Panel and double click Sound. Click on the Sounds tab. You'll see a list of Windows events (start up, shutdown, log off, etc.). Highlighting an event should show you the sound Windows has associated with this event in the box just below the list of events. If no sound is shown, use the drop down list to select one or use the drop down list above the events list, select Windows Default and click Apply.
Let us know if that helps.
I seem to have lost all sounds associated with Windows Vista (startup / shutdown jingles, message alerts, clicks & pings when changing the volume, etc.). This happened a few days ago at, or around, the time I installed Vista Service Pack 2. I know these sound files are still installed on my laptop because I can play them through a test. But it is as if Windows has forgotten to play them at the correct times.
I also have no sound when viewing videos on YouTube. However, iTunes and Windows Media Player seem to be working fine.
I have checked my volume level, speakers and speaker drivers and they are up to date & apparently working fine. Disabling / Enabling the device has also done nothing.
I hope there is a simple fix to this. I am using a HP Pavilion dv9000 laptop and Vista 32-bit O.S.