I am running windows Vista and have recently started having a problem with the sound. The sound on the computer works fine until yahoo is open and I have logged in. Once that happens, there is no sound produced for the computer. It also only appears to happen with yahoo is opened and used on battery power, but that might just be a coincidence. When I open the sound controls it lights up the bars in the mixer as if sound should be coming out, but nothing. The only way to get the sound to come back is to reboot the computer. Any ideas?