This is the Notebook PC category.
Posting, "....and the VoltageS are correctly on the power supply.....makes me think we are talking about a Desktop PC here.
12 Volts (All DC)
Green color LED (Light Emitting Diode) referred to, is the motherboard power LED.
All the power cables from the Power Supply, plugged into the motherboard?http://www.playtool.com/pages/psuconnectors/connectors.html#atxmain20
What are the voltages of the SMPS? http://en.wikipedia.org/wiki/Switched-mode_power_supply
Post back in a Comment as to the computer manufacturer name, and model number. (Plus questions I asked)
Found on the back for a desktop computer, usually next to the Windows product key; or up on the side of the computer tower (Case)
I have seen some models (Dell) that there is a small front door you open, and the model number is down towards the bottom, on the inside. (Of computer, not door)
While I wait for your reply, in the meantime unplug the power cable to the optical drive (CD/DVD drive), and the harddrive.
Remove the Ram Memory.
Plug the computer back into power. Motherboard LED light on?
We are removing some devices that require power, to see if the motherboard LED power light comes on.
Hold the phone..............or are you referencing to the Green LED light that is on the back of the Power Supply?http://h10025.www1.hp.com/ewfrf/wc/document?docname=bph06788&tmp_task=solveCategory&cc=us&dlc=en&lang=en&lc=en&product=432786
Scroll down a little to the photo. That Green LED light?