It seems like you've done all the possible troubleshooting steps but here are some more that may help.
- Start by doing hard reboot, remove the battery and unplug the AC adapter then press and hold the power button for 20 seconds then try booting it up again.
- Next to try is to reseat the RAM again, remove them all for couple of seconds then try booting it up again.
- If it will still not work, remove the battery and see if it will boot up with just the battery connected.
- Do try a different AC adapter that has the same voltage if the same problem will persist.
- If you'll see lights on the laptop but there's still no display, connect an external monitor and see if you'll get any display from it or not.
- If all these will not work the motherboard is already faulty.
- If the laptop is still under the factory warranty do contact the manufacturer for a repair.