NO LOG ON SOUND ALSO NO STREAMING VIDEO SOUN

Hello,
Can anyone help!....I have no log on or off sounds also when I play streaming video I get the video but no audio.I have tried all the suggestions posted so far and still no audio.No yellow marks in device manager,no red x either all sound devices apear to be functioning correctly.I did diagnostics with dxdiag and all sounds ok.I went in to sounds and audio devices,properties clicked on audio,under sound playback is:soundmax digital audio,checked volume all ok ( by the way ,I uninstalled soundmax and re installed it from dell"s download site ) I have tried to follow instructions from microsoft and dells support sites as to how to get my log on and off sounds back but there is a problem.According to them I should open my sounds and audio devices,click on sounds and under program events pick any of them such as asterisk and click the play symbol beside it,however the symbol is not highlited and can not be clicked.My system is a dell dimention 3000 and iam running windows xp home,if any one has a similar problem and found a solution please respond.P.S I can play a dvd or cd and no problem, also I can play all the songs I have in My I tunes without any audio problems.