Now, restart, go to BIOS/Advanced and set onboard audio to OFF or Disabled (depending on BIOS options).
Log into Windows and see if anything changes. With little chance, this may help.
BTW, when you play music with Windows Media Player, does it report any errors, crash, or everything is OK except that there's no sound from speakers?
My next steps would be:
1. Right-click on Windows system disk (most probably it would be C:\) and click on Disk Cleanup... follow the procedure. Remove all files you don't need, especially temp.
2. Install Intel drivers. Reboot.
3. While restarting, enter BIOS and set onboard Audio to ON/Enabled.
3. Install DirectX 9c. Reboot.