Question buzzing noise coming from fan when holding power button

[djeuro1981]

hi guys
i have a clients macbook pro here mid 2012 and i have never seen an issue like this before, what happens is if you press the power button once the processor fan shakes for a second then nothing, if i hold my finger down on the power button the fan will spin but nothing happens no lights no display or anything but also i can hear a faint buzz noise coming from fan area??
Things i have done already (removed hard drive, removed ram) still the same

 

[djeuro1981]

i just stripped down the macbook and re applied thermal paste but nothing still the same (push power button once fan shakes..hold power button down and fan spins but makes a weird faint buzz noise)

 

[djeuro1981]