Lenovo G700 randomly shuts off

I have an old G700 notebook from Lenovo which randomly shuts off.

It doesn’t matter if it’s under load or just idling.

No bluescreen, no warnung. It just shuts off like someone is pulling the power cord.

Also it doesn’t matter if booted into Windows or just idling in the Bios.

Temps are fine.

What I’ve tried so far:

- Replaced Mainboard

- Replaced CPU

- Replaced RAM

- Replaced HDD

- Removed Optical Drive, WiFi Card and Keyboard

- Disconnected the little board with the power/reset buttons on it

- Tried with Battery only

- Tried with Power Cord only

- Tried with both Battery and Power Cord

So pretty much all the main parts were replaced and some optional parts were removed.

Issue still persists.

The only thing left untouched is the display which runs fine.