Interesting sound problem

I have a computer I just installed a used Compaq Presario SR1123WM motherboard to replace an old eMachine board that died. The hard drive had a previous install of WinXP Home. After I got everything up and running and Windows re-activated, everything worked fine, except the sound. I have installed the drivers from the HP site (original, then the updated drivers). No matter what I do, no sound comes out.

Here are things I've tried:
-tested speakers on another computer (they work fine)
-tried all the sound ports on the motherboard (just as an idiot check)
-uninstalled and reinstalled the drivers
-upgraded to Windows XP Pro (everything but audio works)
-setup and logged in remotely using Remote Desktop and the sound comes through on the remote computer
-disabled the onboard audio device and installed a PCI audio device and still no sound.

I am just blown away, especially considering the sound comes through remotely and the PCI card doesn't have any sound come through. Any thoughts?