No audio device

My system is Compaq Evo D380mx, P4 1.66, Intel 845g, 512MB RAM, integrated AC97 audio, XP-pro SP2, WMP10. So far (last five years) audio has played smooth. Just had to replace the heatsink fan ... got a technician to do it. After that windows sounds (start / shutdown) did play, and I did not check any music. Later, WMP refused to play music. Device manager shows all ok, but control panel > sound properties > volume says "no audio device". Now, even the windows sounds are not coming.

In device manager, "Sound, video and game controllers" include :-

Audio codecs
Legacy audio drivers
Legacy video capture devices
Media control devices
MPU-401 compatible MIDI device
Standard game port
Unimodem half-duplex audio device
Video codecs

I am also pasting below extracts from scan by Everest (in early 2007) and now, side-by-side. Shall be grateful for guidance.

Thanks for help.

================================================

Earlier : Audio Adapter Intel 82801DB ICH4 - AC'97 Audio Controller [A-1]

Now : Audio Adapter Modem #2 Line Playback

-------------------------------------------------------------

Earlier : [ South Bridge: Intel 82801DB ICH4 ]
AC'97 Audio Controller:
Audio Controller Type Intel 82801DB(M) ICH4
Codec Name SigmaTel STAC9750/51
Codec ID 83847650h
S/PDIF Output Supported

Now : [ South Bridge: Intel 82801DB ICH4 ]
Audio section missing

-------------------------------------------------------------

Earlier : Windows Audio
Device Identifier Device Description
midi-in.0 0001 0067 MPU-401
midi-out.0 0001 0066 Microsoft GS Wavetable SW Synth
midi-out.1 0001 0066 MPU-401
mixer.0 0001 0068 SigmaTel Audio
wave-in.0 0001 0065 SigmaTel Audio
wave-in.1 0001 0050 Modem #1 Line Record
wave-out.0 0001 0064 SigmaTel Audio
wave-out.1 0001 0051 Modem #1 Line Playback

Now : Windows Audio
Device Identifier Device Description
midi-in.0 0001 0067 MPU-401
midi-out.0 0001 0066 MPU-401
wave-in.0 0001 0050 Modem #2 Line Record
wave-out.0 0001 0051 Modem #2 Line Playback

-------------------------------------------------------------

Earler : PCI / PnP Audio
Device Description Type
Intel 82801DB ICH4 - AC'97 Audio Controller [A-1] PCI

Now : PCI / PnP Audio section missing

-------------------------------------------------------------

Earlier : [ SigmaTel Audio ]
DirectSound Device Properties:
Device Description SigmaTel Audio
Driver Module STAC97.sys

Now : [ SigmaTel Audio ] section missing

-------------------------------------------------------------

Earlier : PCI Devices (included)
Bus 0, Device 31, Function 5 Intel 82801DB ICH4 - AC'97 Audio Controller [A-1]

Now : PCI Devices (includes)
Above line missing

-------------------------------------------------------------

Earlier : Device Resources (included)
Resource Share Device Description
IRQ 17 Shared SigmaTel C-Major Audio

Now : Device Resources (includes)
Above line missing

Hi abanerji and welcome to Dev Shed.

It sounds like the on-board sound card may be disabled in the BIOS. Have a look in there and ensure that it is set to 'enabled'.

I recently restored my E-Machines computer completely. I do not have any sound. In the Device Manager it says that all installed audio devices are working properly (Legacy Audio Device, Codec, ect.). I have went into BIOS Settings and the plug and play is enabled. I can not seem to get Windows Update to work, it says checking computer for updates and the progress bar does nothing (I have left it for hours and nothing). It is set to automatically update daily but I dont think it is?! I am running Windows XP Professional 2002 with Service Pack 2. I am sorry this is being posted as a reply, could not figure how to post. The computer works fine now except for the sound. All three sets of the speakers we have tried work fine.
Thank you,
Johnny