Laptop does not turn on accept the green led steady on

Please can some one help me out, i hope i have made it clear as to what sort of problem im experienced at my laptop.

I have a Sony Vaio vgn-fz31s, i have change the motherboard due to previous motherboard broke down. when i plug the AC adapter to charge or to boot the laptop it wont boot.

if i press the power button to boot, led power comes on green and stays steady green while the battery lights is flashing normal.

even if I remove the battery and trying to boot without the battery the same problem the power led comes on and stays steady green.

I have tried with the battery, without AC adapter power it does the same thing the led power stays on and the battery led.

when i try it to boot it without battery, just with the AC power, once i press the power button to boot the green lights come on it remains steady on, if i keep repeating on pressing the power button then the battery light comes on and goes of even thou the battery is not plug it.

Thanks in advance