The chipset fan may already be attached, but it should be replaceable (it would be a very poor design to hardwire it in, anyway).

With the previous fan problems that puts heat as the most likely problem. <img src="/ubbthreads/images/graemlins/cry.gif" alt="" /> However, if you can scavenge another power supply, that would be much easier and cheaper to check first than a new motherboard.