No Power on Led 1 Green

So, a friend bring me this iMac and he told me that first it gave him trouble to power on, but he waited for some minutes and then it boot up fine. Now it does not power on at all.

So I take it a part, I clean it up (it was pretty dirty) and then I tried to power it on, nothing happened.

The Led 1 have a green light on, check the button and its OK, I short the pads and nothing happened, but it give me 12V in pin 11 of the test point (as it should when power on button its pressed) but still no power on.

I check the schematics and started testing the power rails:

S5 rails are on when unit has AC Power, I check all the S5 rails and they are OK

can´t check S3 nor S0 rails because they are on when logic board its power on.

Does anybody have any ideas?????

Thank you!