@pjotrlen could be as simple as a blown fuse to as complicated as a blown component that might be hard to identify. First step would be to disassemble your Thinkpad and check the motherboard for any missing, charred or otherwise damaged looking component. you can download the maintenance manual [https://support.lenovo.com/de/en/manuals/um019141|from here] which will help you to work on it. [br]
After that, post some good pictures of your motherboard with your QUESTION. That way we can see what you see and hopefully help you further. [guide|21499]