Unable to listen songs on external and internal speaker?

[Cap2010]

Have a Sun Blade 1000 Desktop and installed xmms and workman
application from the CD given on purchasing of SUN system.

Earlier, we were getting sound (can hear)
from internal and external speaker on playing any audio CD or mp3 songs.

Now, don't know what happened, unable to hear or get sound from the system.

I am able to play xmms(winamp) and workman application, in xmms (winamp)
can see the graphic display and have kept max. volume.

Only thing is when playing xmms it display an error message
unable to detect sound card.
Thereafter, it plays the songs but can't hear or not getting sound.

Have checked audio control from desktop and found that volume is full; line input, internal speaker
headphone all are clicked (are active) plus it is not muted.

- How do i Check
1) Whether sound card is there or not.
2) Whether package for sound card is there or removed.
3) Which file should i check for sound system is ok

- What else should I check to confirm that sound card is there and package for the
same is also there.

- Or is any file is removed or changed.

- How can I change the driver / sound card from the application.

Please help.

Cap