Emachines T3516 - no sound

I'm trying to fix my brother's computer. I don't know what the hell he did to it, but in trying to remove a virus, he "lost" his sound.

The computer is an Emachines T3516 with a RC410-M rev 1.1 mobo. The driver that used to be installed was Sigmatel C-major Audio. I found the drivers on the emachines website: http://www.emachines.com/support/p [...] odel=T3516
However, when attempting to install it, I receive a "Device Object not present, restart the system and run the setup again" error. Restarting the system doesn't help.

Sounds and Audio Devices Properties dialog box from Control Panel indicates "No Audio Device".

Device Manager shows a big yellow question mark for Audio Device on High Definition Audio Bus". Attempting to install the driver from there, pointing at the installation folder from the emachines driver above fails with "The hardware was not installed because the wizard cannot find the necessary software".

I've seen several posts on the web where installing the Windows hotfixes KB888111 and KB835221 worked for some people. I tried that, too, but no joy.

Can anyone help me out here??