What marking are there on the motherboard? Do you have a picture to post up?
If it's a standard PC motherboard you should be able to track down a manufacturer and simply pick up one on eBay.
Also, check the electrolytic caps in the area around the CPU's voltage regulator. Do any have split tops, are they tilted, or have they blown the rubber plug out the bottom? If so, replacing the caps can bring new life to it.\
PCB problems and fixes