Your first problem is, you bought an HP. Companies like HP and Dell and Gateway seem to have their MB's specially made. Evidently, so they can take stuff away from them - like AGP slots - so you can't buy their cheap computers and upgrade them later; they want you to spend much, much more just to get options you should've gotten anyways.
Your motherboard is OEM and not supported at all by the company who made it... I'm not even sure who that is. On OEM parts, HP - or whoever the company that is manufacturing the final product-accepts the support function of it, but it sounds like you ran in to a deadend with them.
For example, if you buy a Chevrolet, GM supports any problems you might have with it's transmission which may have actually been made by some Korean manufacturer you can't pronounce.
Yellowstone is not the manufacturer of the MB, its actually just a codename. If you are even able to find out who the manufacturer is, and you give them that codename or model number, they'll probably just tell you that you have to speak with HP anyways.
Ahh... globalization... ain't it purty?