MacBook dead after SSD upgrade

Hey all, I have tried to upgrade my MacBook with an SSD. I have opened the back plate, disconnected the battery cable, removed the HDD and inserted SSD. After that, the MacBook was dead. There is nothing, no fan spin, no beeps, no lights, nothing. I have tried with the old HDD and it’s the same. Dead. The only light I get is from magsafe.

I have tried booting it up with no battery, with battery and magsafe, with HDD, SSD I have disconnected the keyboard, RAM, … don’t know what else I can try.

Anyone have any idea where the problem could be?

Thanks