No sound/audio playback device?

Something weird's happened to my computer (a 4/5 year old Dell laptop running XP).

For some reason, when i clicked on iTunes to play some music today, i got a message saying iTunes has detected a problem with your audio configuration.

I clicked on the 'speaker/volume' icon in the bottom toolbar and got this message:
No active mixer devices available.  To instal lmixer devices, go to control panel, click printers & other hardware, then install/add hardware

But i have no hardware to install! 
The sound was working fine yesterday... i've not 'done' anything to it, or changed anything.

I clicked on Sounds & Audio Devices in the control panel, but it won't let me adjust or tweak anything -- just displays a no audio playback device message.

Any ideas?
I'm admittedly clueless on this kind of stuff, so any help would be most appreciated!

Sounds like there's a problem with the driver.  Try looking in your Device Manager dialogue (right click on My Computer-> Properties.  Then under the Hardware or System tab --> Device Manager...it should be on the top).  In here, first check to see if any items have exclamation points next to them.  If the do, right click on it and try to update driver.  If that doesn't work, try rolling back the driver.  If all else fails, use the force (of a hammer).

Another thought would be just to do a system restore back to yesterday. I've done it with my desktop running XP with the same problem but I am not sure if your laptop has this function. Just an idea.

Thanks for the tips! 

Same thing happened to my laptop and I did what impleri suggested and checked the driver...it threw up an error code.

I searched the net for the error code and "how to fix".  The reason that it happened to me was because of a iTunes upgrade which corrupted the driver.  Once I unistalled that programme and did some other checks as per the online help suggested..re-booted the system and it worked fine..sound came back ok.  I then re-installed Itunes no problem after that.

Hope you get it fixed