I have for some time noticed that the sound icon on my desk top has been disappearing and reappearing. When I needed to switch the sound off it wasn't there so I decided to try and access it through the control panel. Instead of switching it off it became uninstalled. I then checked the status of the device through the Device manager and found i to be there but it was not 'digitally signed'. How do I get it installed and working for me again.