Asus P9D WS - Manual (Page 34)

2-16 Chapter 2: Hardware information
Chapter 2
2.2.6 Onboard LEDs
1. POST State LEDs
The POST State LEDs indicate the status of these key components during POST
(Power-on-Self Test): CPU, memory modules, VGA card, and hard disk drive. If an
error is found, the critical component’s LED stays lit up until the problem is solved.
2. EPU LED
The EPU LED lights up when the EPU switch is turned to Enable.