If you are on XP, check out the soundscheme.
start>settings>controlpanel>sounds speech and audio>"change the soundscheme".
Maybe set it to default if its not already. I tend to turn mine off, so I dont hear websites and downloads 'bonging' cos its a bind if you record music and find you have click's from browsing he net or bong's from errors or whatever mixed in the recording! lol.
See ya
Sirius.