I came across and into the possession of an HP Pavilion zd8300 series laptop. After installing Windows 7 on a blank hard drive disk (HDD), I found out that the audio was no longer working along with two other components. They listed under Device Manager the "Unknown Devices" designation. The audio was listed as "Multimedia Audio Controller" in Device Manager. The two other components were the external storage card reader (SD, MMC, etc...) drive (listed as "Mass Storage Controller") and some phone modem issue (listed as "PCI Modem").
This is a common issue for those installing an advanced/more modern operating system onto an older laptop with a motherboard intended for use with Windows XP or lower.
You'd think that if you found out what your default audio system is for your laptop model, you could find the appropriate software with all the drivers and install it on your laptop and you'd be good to go. Turns out, no matter what driver you pick out, they are all going to fail.
I got lucky and with the help of a friend, I discovered the solution: What you need to do is manually edit one of the subfiles from the audio driver file. More specifically, you need to modify the .inf file so as to redirect and point the file to the appropriate physical hardware component on your laptop by changing and updating the listed hardware IDs with your own IDs. After you install the driver manually through the device manager, your laptop should operate as intended.
Of course, I have since corrected my own audio issue for this laptop but was unsuccessful using a similar procedure to fix my external storage card read drive (Micro SD, SD, etc...).
I am still searching and trying various alternatives to fix that issue.
This is not a guaranteed fix for your issue for there could be a host of other issues blocking resolution of the problem or that you audio system is simply physically damaged.
You may also want to check to see if a line is simply disconnected.
This post is not written with extensive detail nor with an in-depth, step-by-step guide towards fixing your issue primarily due to the very limited audience who still have, using, and since upgraded their operating system of this specific and outdated laptop model. If you would like further assistance, please comment and I can, of course, provide additional information.