I don't know if a socket 942/AM3 is old enough, but...

Some time ago, my wife's computer mainboard died and it's been laying around since then. The board is an Asus M5A99X EVO (rev 1.01), fitted with 16Gb RAM and AMD FX CPU. When powered on, it doesn't run and it lights CPU_LED. It has no obvious signs of failure: No bulged caps (caps are metallic), no signs of leakage and no broken/burnt chips (although all the VRM area is covered with a blue heatsink). Removing all RAM has no effect (in many boards, removing all RAM causes it to beep like crazy... a fast way to check CPU/mainboard).

What can I do to diagnose (and fix if possible) that board?

Thanks.