No sound in Dell XPS13 with Ubuntu 14.04

I have a brand new Dell XPS13 Developer Edition, that came with Ubuntu 14.04, and sound stopped working from one day to another, both in speakers and through headphones.

I'm unable to think what the origin of the problem might be, since from the day it was working to the following day when it wasn't, nothing was installed/deinstalled/upgraded/changed.

It's not a hardware problem, because I tested booting Mint from a USB and sound was working.

Following the Ubuntu troubleshooting procedure (help.ubuntu.com/.../SoundTroubleshootingProcedure), I can give the following hints towards the problem,  but don't know what to do. Any help is much appreciated.

1) when running:

killall pulseaudio; rm -r ~/.config/pulse/* ; rm -r ~/.pulse*

I get no such file or directory error for:  ~/.pulse*

2) Computer is up to date; however running:

ubuntu-support-status --show unsupported

showed some (I think) sound-related packages among them, such as avahi, alsa-mixer, or pavumeter.  I think these somehow unsupported necessary packages is the source of the problem.This is the complete output of the command:

Unsupported:
avahi-discover biz-vivid-skl-meta bt-intel8260-firmware
btusb-iwlwifi-intel8260-dkms camera-app compiz-plugins dino2-meta
gnome-alsamixer gstreamer0.10-fluendo-mp3 gstreamer1.0-fluendo-mp3
gwakeonlan heirloom-mailx icedtea-6-plugin kbibtex libevdev2
liboil0.3 libqdjango-db0 libusermetricsinput1 linux-headers-3.19.0-58
linux-headers-3.19.0-58-generic linux-image-3.19.0-58-generic
linux-image-extra-3.19.0-58-generic
linux-signed-image-3.19.0-58-generic mesa-utils
oem-alps-touchpad-1521052-dkms oem-audio-hda-daily-lts-vivid-dkms
oem-workaround-poweron okular-backend-odp padevchooser paman paprefs
pavumeter pdfshuffler pulseaudio-paths-backport python-poppler
python-pypdf python3-progressbar qtdeclarative5-usermetrics0.1 r-base
r-base-core r-base-html r-cran-boot r-cran-class r-cran-cluster
r-cran-codetools r-cran-foreign r-cran-kernsmooth r-cran-lattice
r-cran-mass r-cran-matrix r-cran-mgcv r-cran-nlme r-cran-nnet
r-cran-rpart r-cran-spatial r-cran-survival r-doc-html r-recommended
synaptic-i2c-hid-3.13.0-32-backport-dkms unity-greeter
usermetricsservice wifi-intel8260-firmware
xserver-xorg-video-s3-lts-vivid

4) I also run the Alsa diagnostic command:

wget -O alsa-info.sh www.alsa-project.org/alsa-info.sh && chmod +x ./alsa-info.sh && ./alsa-info.sh

which showed that no soundcard is being found.... Here is the complete output:

upload=true&script=true&cardinfo=
!!################################
!!ALSA Information Script v 0.4.64
!!################################

!!Script ran on: Sun Apr 24 15:37:03 UTC 2016

!!Linux Distribution
!!------------------

Ubuntu 14.04.4 LTS \n \l DISTRIB_ID=Ubuntu DISTRIB_DESCRIPTION="Ubuntu 14.04.4 LTS" NAME="Ubuntu" ID=ubuntu ID_LIKE=debian PRETTY_NAME="Ubuntu 14.04.4 LTS" HOME_URL="http://www.ubuntu.com/" SUPPORT_URL="http://help.ubuntu.com/" BUG_REPORT_URL="http://bugs.launchpad.net/ubuntu/"

!!DMI Information
!!---------------

Manufacturer: Dell Inc.
Product Name: XPS 13 9350
Product Version:
Firmware Version: 1.2.3

!!Kernel Information
!!------------------

Kernel release: 3.19.0-58-generic
Operating System: GNU/Linux
Architecture: x86_64
Processor: x86_64
SMP Enabled: Yes

!!ALSA Version
!!------------

Driver version: k3.19.0-58-generic
Library version: 1.0.27.2
Utilities version: 1.0.27.2

!!Loaded ALSA modules
!!-------------------

!!Sound Servers on this system
!!----------------------------

Pulseaudio:
      Installed - Yes (/usr/bin/pulseaudio)
      Running - Yes

!!Soundcards recognised by ALSA
!!-----------------------------

--- no soundcards ---

!!PCI Soundcards installed in the system
!!--------------------------------------

00:1f.3 Audio device: Intel Corporation Device 9d70 (rev 21)

!!Advanced information - PCI Vendor/Device/Subsystem ID's
!!-------------------------------------------------------

00:1f.3 0403: 8086:9d70 (rev 21) (prog-if 80)
 Subsystem: 1028:0704

!!Modprobe options (Sound related)
!!--------------------------------

snd_atiixp_modem: index=-2
snd_intel8x0m: index=-2
snd_via82xx_modem: index=-2
snd_usb_audio: index=-2
snd_usb_caiaq: index=-2
snd_usb_ua101: index=-2
snd_usb_us122l: index=-2
snd_usb_usx2y: index=-2
snd_cmipci: mpu_port=0x330 fm_port=0x388
snd_pcsp: index=-2
snd_usb_audio: index=-2
snd_hda_intel: jackpoll_ms=500

!!Loaded sound module options
!!---------------------------

!!ALSA Device nodes
!!-----------------

crw-rw----+ 1 root audio 116, 1 Apr 24 17:34 /dev/snd/seq
crw-rw----+ 1 root audio 116, 33 Apr 24 17:34 /dev/snd/timer

!!Aplay/Arecord output
!!--------------------

APLAY

aplay: device_list:268: no soundcards found...

ARECORD

arecord: device_list:268: no soundcards found...

!!Amixer output
!!-------------

!!Alsactl output
!!--------------

--startcollapse--
--endcollapse--

!!All Loaded Modules
!!------------------

Module
dell_wmi
sparse_keymap
ctr
ccm
nvram
snd_seq_midi
snd_seq_midi_event
snd_rawmidi
snd_seq
snd_seq_device
snd_timer
snd
soundcore
msr
arc4
x86_pkg_temp_thermal
coretemp
dell_laptop
dcdbas
kvm_intel
kvm
crct10dif_pclmul
crc32_pclmul
aesni_intel
aes_x86_64
lrw
gf128mul
glue_helper
ablk_helper
cryptd
iwlmvm
uvcvideo
dm_multipath
videobuf2_vmalloc
videobuf2_memops
videobuf2_core
joydev
mac80211
v4l2_common
videodev
serio_raw
scsi_dh
media
iwlwifi
i915_bpo
cfg80211
shpchp
intel_ips
drm_kms_helper
drm
i2c_algo_bit
i2c_hid
hid
int3403_thermal
int3400_thermal
acpi_thermal_rel
acpi_pad
intel_hid
mac_hid
cmac
rfcomm
bnep
parport_pc
ppdev
lp
parport
nls_iso8859_1
btrfs
xor
raid6_pq
dm_mirror
dm_region_hash
dm_log
btusb
btintel
bluetooth
compat
psmouse
ahci
nvme
libahci
wmi
video

!!ALSA/HDA dmesg
!!--------------

Any help is very appreciated.