Optiplex 870 Sound Problem

Hi,

I'm experiencing an sound issue on my Windows 7 x32 Computer.

in the systray, the speaker icon is red crossed with this message " no audio device is installed"

In the device manager everything seems to be OK (no warning or error displayed)

I tried to uninstall drivers, desable and enable audio device in the manager, update drivers without progress.

I launched the Dell diagnostic tool before the Windows boot and made a custom test on audio device.
There i can here the music test from the speakers.

After the reboot the problem persists, if somebody has an idea to solve the issue, i'll be very pleased.

Thanks a lot

PS: The latest drivers i installed are Analog Devices ADI 198x Integrated HD Audio, v.6.10.1.7280, A11