Will Not Power up

Hey Peeps,

Ive researched as much as i could, but their is no problem similar to mine, well not that i could find through google or through any of the questions made on ifixit, i hope you i can get anyones help? it would be much appreciated, i really dont want to move on to the slim 0_0

now

Im not 100% sure as to how it happened, but according to my little brother who was playing as i was away, played and made an update for MW2, after it had finished, it would not turn back on

so

Problem:

PS3 has the red light as soon as i turn on the AC power switch on the back,

As soon as the power button is pressed, it disappears and nothing happens

try turning the AC switch on and off, red light dosent come back at all

Solutions attempted:

• replacing the power supply unit
• old 40GB PS3 hard drive (unformatted)
• new AC power cord

After Replacements were made:

AC switch on, Red light would appear, i press the power switch its goes green for one second then disappears and never comes back again

Where im stuck:

Is it the YLOD?

Is the motherboard fried?

Should i replace each and every part that could relate to the problem?

ive read replacing the ejection button ribbon cable might help? (which ive ordered)

Any help would be awesome!

Cheers

John