I've installed the OSS backend from a deb64 package. And the sound in ubuntu is disappeared... Seems the audio card (hda nvidia) is not recognized anymore... What can I do?
EDIT
Sound now works, but OSS still don't... It seems to work not very well with ubuntu (also if it is shown in control panel).
OSS is no longer supported by Ubuntu
Canonical/Ubuntu has chosen to disable OSS support in their kernels and ignore any bugs filed against OSS4 packages. If you're considering using OSS4, you should probably use another Linux distro like Arch Linux.
It also may be likely your hardware does not support OSS, you can find the list of supported hardware here
If you really want to try to install and get OSS working you should have a read of the Ubuntu Wiki Documentation for OpenSound
