Windows 7: Audio configuration no audio output devices?

my computer's sound has stopped. I have searched through lots of websites looking for help.
I first noticed this problem when I tried to open iTunes and it came up with the message 'iTunes has detected a problem with your audio configuration. Audio/video playback may not operate properly'. I also cannot listen to music or things online either.
I have looked at my computer's device manager and can't find any catergory such as 'sound, video and game controllers', which one site suggested to try and check the sound card. I have also tried to update quicktime but that did nothing. I have also tried looking at 'sound' and under both the playback and recording columns it says that there are no audio devices installed. THis appears to be the common phrase along a problem with the audio configuration.
This has not ever happened to my computer before and I have had it for about 3 years now. It is a toshiba laptop with windows 7 home premium.
Please help guys, I am really frustrated.

If its not being detected at all in the Device Manager, it will not show up anywhere else.

When you boot up your PC, enter the BIOS (could be called "Setup") and check to see if the sound is disabled. If it is disabled in the BIOS it will not show up in Windows. If its showing as enabled in the BIOS, do a BIOS reset (to factory setup) and see if that makes a difference.

If its not disabled in the BIOS there is a chance the hardware has failed.

Where do you enter the BIOS?

When you first power on, one option will be to enter the BIOS. Some PC's use F2, some F10, some the "DEL" key. Not sure what your Toshiba uses, one that I found doing a search uses F2. Usually its listed on the screen what key to press. The screen goes by fairly fast so you have to be quick.

what do you press then? i have found the setup by pressing F2 but then what do I press? there is nothing about sound or audio.
Also, the computer says the problem is in the directX/WDM. not sure what that means but hope you can help

It is more than "directX/WDM". Since its not listed in the Device Manager, it means that either a hardware problem has caused the sound device not to work and/or its disabled in the BIOS.

The sound must be enabled in the BIOS or it will never be detected by Windows. However, if its enabled in the BIOS but Windows is still not detecting it, this suggests a hardware failure.

I may be best to have a qualified computer tech look at it as the next step.