sound problem

I have a 810e motherboard and i am using its onboard AC97 sound. It had been working fine till i took it to my friend's place he had an earthing problem and when i connected my pc since then i have not been getting sound. My windows xp detects it and i can even play music but just no sound. cheked every damn thing. My friend's pc works fine though. I even formatted my drive and installed xp again it detects the sound i, when i speak into the mic the voice level in the display moves indicating its taking in the sound input. Its just the there is no sound output. What can be the problem, is the sound card gone?

sounds like the output is fried, but go to the control panel, switch to classic view, go to sounds and audio devices, on each of the tabs make sure all the devices show your sound card the 97' synth. stuff, now bring up the volume controls, make sure all the sliders are up and none are muted, but xp would have installed this card by default, and the sound should atleast work. so like i said output is probaly fried. check the device manager for any yellow ! or ? also