Hi,
Thanks for posting in Microsoft TechNet Forum.
Can your computer detect the sound card in Device Manager? Generally, if the computer can't install device drivers, it can be related to either device driver or motherboard version. I recommend that you update your BIOS and make sure that your motherboard supports these audio devices in Windows 7. To do this, please refer to Asus site to obtain the latest BIOS.
M4A78 PLUS
http://support.asus.com/download/download.aspx?modelname=M4A78 PLUS&SLanguage=en-us
Note: we provide this third party link for downloading related driver. There may be some changes without notice, Microsoft doesn't guarantee the security in this website.
By the way, it is also recommended to check hardware compatibility in Windows 7 Hardware Check Site.
Hope this helps. Thanks.
Dale Qiao