When you try to play audio does the sound level meter move with the volume? (In windows 7/Vista just click the volume icon when something is playing and on older OS you will have to look in the sound menu) If it's not registering the audio is being played (not moving) then it's a software issue.
If this is a recent problem the you can launch your laptop from the "last known good configuration" if you are using windows, won't affect personal files but won't fix driver issues (might work if it's a system issue), if you set a prior windows back-up point you can also launch from that which should fix the problem if it's not hardware related. (just remember to back-up new data).
And if all else fails then, back-up your data and restore the system or call tech support (I would restore system :P)
Common problems (Worth Double Checking):
Corrupt Driver
Incorrect Driver
Mute is on
Devices Disabled (Or incorrect Config.)
Hope this helps.
