Hi I am new to the forum...I just installed Windows Vista and it show the volume icon and says: " No audio output device is installed"....I have a dell dimension 8400 computer....is there is someway to fix this please help me, it would be very sad to have to change back to XP because of the audio

I had this exact problem. I had a SigmaTel Audio. The switch from XP to Vista somehow corrupted my audio; I couldn't hear anything! I reinstalled the audio driver (it doesn't matter whether you dowload the one for vista or xp, either will work since it is the vista installation, not the actual operating system which wasn't compatable w/ the audio driver.) from the dell website. After all of this, after it said there was audio coming out, there wasn't. So I simply tried using new speakers-and viola! Problem solved.
Also: I have a Dell Dimension E520. I now use Vista Home Premium.

somewhere out there i read that microsoft screwed up all sund cards with vista, since vista only plays certain kinds of sound files...

though i solved my problem by downloading brand new vista-compatible drivers for my creative sound card from the site...
maybe if you search for vista-compatible drivers for your sound cards...

Why do you think that?
Vista (the actual OS) does need drivers that are designed for it. I had to download the Vista set from RealTek in order to get my machine to stop crashing everytime I tried to use enhancements.

most of the time, when you install vista you need to download drivers compatible with vista, since, as i said, they messed up sound drivers... maybe intentionally...