Info required about the green light on the back of my Desktop PC

Hi everybody,
There is a green light above where the power lead is inserted at the back of the PC that comes on for a few seconds and then turns off each time I turn on my power strip... before pressing the power button on the PC. Every few boots this light sometimes stays on for 30 seconds. When this happens the ethernet connection also lights up at the back of the PC before both the green light and the ethernet connection light turn themselves off. Any idea why this happens?

Yeah Its just above the power socket. Not sure what PSU type is but its a 3 month old Dell system. I think its 290 Watts. The green light is on all the time when the PC is switched on. It does have a diagnostic button at the side of the light. I don't know what that is for either. Ive never touched it lol

CountMike said:

Main connector from PSU to motherboard (usually 24 pin) has one wire coded Gray color, provides signal called Power_good between MB and PSU which signals PSU to give full power to system. That's what light shows. There is power to MB as soon as PSU is turned on and plugged in (5v to certain parts) without which ATX type of system can not start.

Thanks Mike for the info. I was curious as to what the green light at the back of my PC indicated. Now I know