built-in microphone not working on sl500 with Vista

[2nat]

I have an integrated camera and I suppose that built-in microphone is a standard on sl500 - but when I go to:
Control Panel - Sound - Recording tablet - there is an info: no audio devices installed
buttons Configure / Restore defaults / Properties are non-active

I have already tried to reinstall audio drivers from Lenovo support site (and some others) with no result.

Any idea what to do?
I would be grateful