I can't get the sound working om my pc. I've read lots of threads on this forum about sound but no answer to my problem.

I can see my soundcard:

aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: HDMI [HDA ATI HDMI], device 3: HDMI 0 [HDMI 0]
Subdevices: 1/1
Subdevice #0: subdevice #0

Starting alsamixer gives me:

|Card: HDA ATI HDMI                                   F1:  Help               │
│ Chip: ATI R6xx HDMI                                  F2:  System information │
│ View: F3:[Playback] F4: Capture  F5: All             F6:  Select sound card  │
│ Item: S/PDIF                                         Esc: Exit               │

│                                     ┌──┐                                     │
│                                     │OO│                                     │
│                                     └──┘                                     │
│                                  < S/PDIF >                                  │
│                                                                              │
aplay gives me this:
ALSA lib pcm_dmix.c:1018snd_pcm_dmix_open) unable to open slave
aplay: main:660: audio open error: No such file or directory

If i go to gnome control centre the is no hardware device and is ouputs:
(gnome-control-center:2013): sound-cc-panel-WARNING **: Failed to connect context: Connection refused

What other checks can I do? Who can help me?