I apologize for reviving an old-ish thread, but I'm running into the exact same issue here, and going through the lenovo support site, the only thing related to Hotkeys I can find is the "Hotkey Features Integration", which I do have installed. After a reboot it still does not work.
I enabled the volume change beep in the BIOS, and the beep goes off, but nothing happens in the OS.
I re-ran the installer, which shows I have the current version of all items, including the System Interface Driver and the On Screen Display. I re-installed both of those and rebooted and still neither the volume buttons or the OSD work.
Any other thoughts? Is it possible they broke something in newer versions of the drivers?
Well, I'm not exactly sure what I missed, but I did resolve it by running the Thinkvantage update. It found some missing packages, and looking at the descriptions, none of them really seemed to indicate it would fix my issues, but after it was all said and done, everything works properly...