Here are some troubleshooting steps that may help.
- Start by doing a hard reboot, remove the battery and unplug the AC adapter then press and hold the power button for 20 seconds then see if it would boot up normally.
- If these doesn't work, do check the AC adapter if it's supplying enough voltage or try another AC adapter that has the same voltage and see if it will boot up normally.
- Next is to reseat the RAM if using a different AC adapter will not work. Remove them all for couple of seconds then put them back in making sure everything is seated properly.
- Another step you may want to try to check if the LCD is okay or not is to connect an external monitor and see if you'll get any display from it.
- If all these doesn't work you may need to open your laptop again then check all the connections you've taken out just to make sure everything is seated properly.
- Do also try to boot your laptop without the battery connected.
- If all these will not work the problem may lie in the motherboard itself.