Go to this page and type in your product name/number/etc. If you don't know what it is, click below the search box where it says "Guide to Finding Your Product Number" and click on your product, in your case the Desktop PC that contains the motherboard. After you locate your product there should be a place to download the manual. You will need Adobe Acrobat to view in PDF format, unless you already have it there is a place to download it on the site there. http://h10025.www1.hp.com/ewfrf/wc/siteHome?lc=en&dlc=en&cc=us&product=top
I also found the following link, but I don't know if it is the right one because it doesn't have the "-la" on the end. Maybe it is similar enough. http://www.manualnguide.com/dl/560/
I don't know if you have tried contacting the HP (or ASUS) customer support, but that might work too.