...try reinstalling the drivers for the sound card or onboard sound or whatever you use.
I've got an ATI Radeon 9000 with 64mb ram running on a Windows XP box (AMD not Intel) and have recently lost the sound in the TV setting only.
I have normal computer sounds, as well as Windows Media Player, ITunes, etc. but nothing when the TV display is used. Also, the picture is a lot shakier than it use to be and sometimes randomly goes into slow motion.
Not sure when it happened since I haven't used it for a while, but I'm assuming some other program I installed messed things up. When I first tried to launch it, it wouldn't work at all so I reinstalled the ATI software - still nothing. Updated to the most recent drivers, remote wonder software, etc. and got the picture back but no sound. ATI knowledge base offers no solution.
Most recently installed software is graphics related (photo and video editing) and includes ULead Video Studio, Corel Photo Album 6, Ding and all Windows security updates except SP 2 and Malicious tool remover (tried when it first came out but Comcast doesn't like it on reboots).
The only hardware changes made was a Firewire card installed and a new wireless router for use with Vonage.
Any suggestions would be appreciated since baseball season is back and we'll be using the TV more.