Sounds

I have this weird problem with the Windows XP sounds. A while ago when i click Internet links i don't hear the click. A month later i can hear it clearly. I wasn't installing anything at that time. Just today when i start up my computer i heard the start up sound you know the jingle.
My question is that what is wrong with it? Why are the sounds just now popping up?
My question is that what is wrong with it? Why are the sounds just now popping up?