Loss of PC sound after xp reinstall.

After reinstall of win. xp sp2 my PC has lost the onboard sound.My mobo is Intel D845 GLVA.There is no add-on sound card.All other functions of the PC are ok.The summary of my investigations is as follows:1)The Audio is enabled in BIOS and Windows Audio is started in Services.Multimedia audio serviceis not found. 2) There is no YELLOW exclamation mark in Device Manager.All the drivers are installed and all the devices are working properly. 3)In System Information section there are no Problem Devices or Conflicts. 4)However when dialog box of 'Sound and Audio Devices' under 'Sound Speech and Audio Devices' in Control Panel is opened it is displayed that Audio,Playback,Recording etc Devices are not present. 5) Direct X Diagnostic tool shows that there are neither sound devices nor drivers.The Note at the bottom of this dialog box says that there is no sound device and if one is expected then install drivers. Now Syschat Forum Experts are requested to give reasons for the lost sound and further guide me whether I should clean-reinstall Windows xp or install a PCI sound card to regain the lost sound. THANKS in advance to all the Forum Members.