I have win. ME
I checked for the mute being checked "OK"
I reboot after checking plug in back of the board.
I also tried add hardware no luck
I still don't have sound
What else can I try.

Go in Control Panel - System - device manager tab. Check in Sound, video, game controllers to see if your soundcard shows up and if it doesn't have some kind of exclamation sign on it. If it does, try to reinstall the card drivers. Has it worked before, or is it new?

I will tell anyone here that if they are experiencing Windows ME problems, instead of wasting time working with it, to fix it, get another OS, WinXP or go back 98SE anything except WINME, it's the worst operating system ever made,
Microsoft admits this and has therefore stopped all technical support to this product,as they suggest you get rid of it themselves, that should tell you how bad it is, get something more stable.