"No audio output device is installed" on Acer model E-380 after wake up

My uncle just bought a new Acer E-380 Desktop. It came with Windows Vista pre-installed. Along with the system there are two speakers provided by Acer. My uncle works for sometime he left the system turned on. So the system goes to sleep mode on its own. But after wake up there is no sound. It only appears after restarting the system. It is a new system and this looks some kind of problem. I checked the system. After getting out from sleep mode the realtek device disappears. Is this a hardware fault.

I am having a Gigabyte motherboard. I just installed Vista on the same. It has Realtek ALC888 HD audio chip on it. Now in bios everything looks to be perfect. I am getting exactly the same error when the system appear back from sleep mode. There is no sound. I had updated the drivers, made changes to audio settings, etc, but nothing worked. It looks that the the audio driver which is installed is not proper. Later on I removed the audio device through Device Manager. I uninstalled it completely. I reboot it was detected automatically and I used the drivers that I got from Windows Update.

That issue lies with some internal broken codecs. And this is more common in Windows Vista. I have a 64bit Vista OS installed in my system. I am facing the same kind of problem with audio. Before that I was using Soundblaster XFi card in my system. It stopped working on its own. There is no reasonable audio driver which can help you to solve the problem. This kind of issue never appeared in XP. I had disabled the sleep mode settings and just allow the monitor to turn of after a while.