Description:
Sound simultaneously only works in one application.
If to run two apps - eg. mplayer and flash, the sound work in the first runing.

Additional info:
* package version(s)
alsa-firmware 1.0.25-2
alsa-hda-tools-git 20121230-1
alsa-lib 1.0.26-1
alsa-plugins 1.0.26-1
alsa-utils 1.0.26-1
alsamixer.app 0.1-3
alsaplayer 0.99.81-5
pulseaudio-alsa 2-1
alsa-oss 1.0.25-1

* config and/or log files etc.
lsmod | grep snd
snd_intel8x0 22829 0
snd_ac97_codec 89932 1 snd_intel8x0
ac97_bus 874 1 snd_ac97_codec
snd_pcm_oss 33381 0
snd_mixer_oss 12863 1 snd_pcm_oss
snd_seq_oss 24764 0
snd_seq_midi_event 4576 1 snd_seq_oss
snd_usb_audio 82689 0
snd_usbmidi_lib 15548 1 snd_usb_audio
snd_rawmidi 14630 1 snd_usbmidi_lib
snd_seq_dummy 1127 0
snd_seq 41535 5 snd_seq_midi_event,snd_seq_oss,snd_seq_dummy
snd_seq_device 4284 4 snd_seq,snd_rawmidi,snd_seq_oss,snd_seq_dummy
snd_hda_codec_realtek 52309 1
snd_hda_intel 22256 1
snd_hda_codec 83677 2 snd_hda_codec_realtek,snd_hda_intel
snd_hwdep 4746 2 snd_usb_audio,snd_hda_codec
snd_pcm 61470 7 snd_pcm_oss,snd_usb_audio,snd_ac97_codec,snd_intel8x0,snd_hda_codec,snd_hda_intel
snd_page_alloc 5869 3 snd_intel8x0,snd_pcm,snd_hda_intel
snd_timer 14902 2 snd_pcm,snd_seq
snd 44874 17 snd_hda_codec_realtek,snd_pcm_oss,snd_usb_audio,snd_ac97_codec,snd_intel8x0,snd_hwdep,snd_timer,snd_pcm,snd_seq,snd_rawmidi,snd_usbmidi_lib,snd_hda_codec,snd_hda_intel,snd_seq_oss,snd_seq_device,snd_mixer_oss
soundcore 4378 1 snd
usbcore 126730 6 uhci_hcd,snd_usb_audio,uvcvideo,snd_usbmidi_lib,ehci_hcd,usbhid

lspci | grep Audio
00:1b.0 Audio device: Intel Corporation 82801I (ICH9 Family) HD Audio Controller (rev 03)

cat /etc/asound.conf
pcm.!default {
type hw
card 0
}

mplayer ./file.mp3
[AO OSS] audio_setup: Can't open audio device /dev/dsp: No such file or directory
[AO_ALSA] alsa-lib: pcm_hw.c:1293:(snd_pcm_hw_open) open '/dev/snd/pcmC0D0p' failed (-16): Device or resource busy
[AO_ALSA] Playback open error: Device or resource busy
AO: [pulse] Init failed: Connection refused
Cannot connect to server socket err = No such file or directory
Cannot connect to server request channel
jack server is not running or cannot be started
[JACK] cannot open server
[AO SDL] Samplerate: 44100Hz Channels: Stereo Format s16le
[AO_ALSA] alsa-lib: pcm_hw.c:1293:(snd_pcm_hw_open) open '/dev/snd/pcmC0D0p' failed (-16): Device or resource busy
[AO SDL] Unable to open audio: No available audio device
DVB card number must be between 1 and 4
AO: [null] 44100Hz 2ch s16le (2 bytes per sample)

mplayer -ao alsa ./file.mp3
[AO_ALSA] alsa-lib: pcm_hw.c:1293:(snd_pcm_hw_open) open '/dev/snd/pcmC0D0p' failed (-16): Device or resource busy
[AO_ALSA] Playback open error: Device or resource busy
Failed to initialize audio driver 'alsa'
Could not open/initialize audio device -> no sound.

mplayer -ao pulse ./file.mp3
AO: [pulse] Init failed: Connection refused
Failed to initialize audio driver 'pulse'
Could not open/initialize audio device -> no sound.

speaker-test -c 2
speaker-test 1.0.26
Playback device is default
Stream parameters are 48000Hz, S16_LE, 2 channels
Using 16 octaves of pink noise
Playback open error: -16,device or resource busy

Also without PulseAudio.

Steps to reproduce:
Install pulseaudio and edit /etc/asound.conf. Prior to that the sound was not. What to do next i do not know.
Alsa-driver package from AUR does not compile, but support alsa-driver there is in the kernel.