My Dell Vostro laptop comes with Ubuntu 14.04 LTS. Recently I updated my laptop with the updates provided by the OS. The new version of Linux kernel was also part of it. After installation it popped up a dialog with a check box “Disable UEFI secure boot”. I ignored to check this and clicked continue. UEFI secure boot was enabled in BIOS.
Ubuntu failed to detect sound card
After reboot, Ubuntu could not able to detect the sound card. I re-installed alsa and pulseaudio, but there was no use. After searching the Internet for almost 2 hours I could able to figure out the reason. UEFI secure boot will disable modules that are not signed or trusted. It seems pulseaudio and alsa sound drivers are not signed or trusted so on boot they were disabled. Hence Ubuntu could not able to detect the sound card. After disabling secure boot from the BIOS setup, things came to normal. Now sound works on Ubuntu 14.04.
Need to figure out how to enable UEFI secure boot along with sound card working.