Check the 3.3V and 5V "Always-On" power rails. If these are missing, the laptop will not respond to the power button.
If you are searching for a schematic download, you are likely facing one of these common LM495 failure modes: Lm495 Mb 11269-2 Schematic-- Download
Below is a useful technical article regarding the LM4950 schematic, typical application circuit, and design considerations. Check the 3