Sound problem on my Gateway laptop Windows Vista?

My laptop will play the sound from YouTube videos or the songs of the people of my profiles from space, but if I try to play an AVI file no sound. There is also no sound in emmulators game or if I try to play a dvd or aol radio. I can not roll back my system is sufficient to correct this problem. Can anyone give me an idea of something to try to fix this problem? Thanks!

Hi, Try re-installing Windows Media Player You can get it here: – http://www.microsoft.com/windows/windowsmedia/default.mspx You may need the previous version, depending on which system operating you are using. Arnak

Help Me! Windows Vista issue. Does your Vista do this flaw?