Vaio NV105 missing part?

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Hi everybody,

I bought a non-working Vaio PCG-NV105 from someone claiming it never was
opened and stopped working suddently.

When I opened it, I saw a bunch of unplugged connectors (including the
keyboard, soundcard and fan)...

I fixed an issue on the power board and now the green light would turn
on, fans and HDD spin, but nothing else happens (no sound, no screen).
I tried to change the CPU, but still the same.
Removing the RAM and all devices: no luck.

I noticed an empty connector on the motherboard. I wonder if some
micro-board is missing (Bios chip?).
It's located on the motherboard, you can access it by removing the
keyboard, through a hole in the shield.
It's written "A B C D" above it, and something like "cn3001" bellow it.

Can someone give me some hardware documentation so that I can check what
this connector is for?
Or even better, can someone tell me if it's the Bios place and where I
can get a replacement one? (worldwide)

Any help would be greatly appreciated.

P.S.: what is the use of the connector on the bottom of the laptop,
hidden by a cover, which is locked by a screw and the memory cover? I
have nothing plugged in it... Is that a diagnosis connector designed for
maintenance tech?

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