After installing Windows 7, everything was fine except sound. It seems like sound drivers were installed correctly but it wasn’t.

You did try to download drivers from lenovo site and install them but shit(!), software installer says that I have no idea about your operating system.

Here are the instructions (applies Soundmax, no idea about Realtek (Xavi reported it works for Realtek too, thanks Xavi!)):

1. Don’t worry. :p
2. Download driver.
3. Installer will extract the package the path you choose (default is C:\Drivers\WIN\Audio).
4. Open Device Manager.
5. Go to Sound, video and game controllers section.
6. Select currently installed device and right click.
7. Select Update Driver Software.
8. Select Browse my computer for driver software.
9. Select Let me pick from a list of device drivers on my computer.
10. Click Have Disk button.
11. Select the location where you have extracted package (#3) and browse <path>i386\Vista folder (amd64 for 64bit).
12. Select the inf file.
13. Click Next;

And you are done!