VAIO PCG-F690. Need help

PCG-F690. Heatsink had visible dust so notebook was hot making a lot of noise by CPU fan. I cleaned it up and now my notebook does not turning on.
The notebook is quite old so the repair in a service center could cost more than to by the same but working one. So I want to try to repair it at home. I would be very much obligated for any recommendations here.

What did I do. I turned off the top part including the buttons block, keyboard and touchpad section. Then I removed the heatsink, cleaned it with a brush and changed the thermal grease. Finally I turned all back, turned on external power and realised that nothing could turn it on now. Having this problem I deeply disassembled the notebook even removed CPU and investigated the boards. I didn't find any external objects, broken parts etc there.
Finally I can add that the external power supply is Ok - 19.5V and that there were no problems with the notebook except the noise/temperature before the operation.

Thank you in advance for any help/recommendations.

 

Double check again, make sure you plugged every cable back in. It's an easy mistake to make.