Please do try these troubleshooting steps that may help in solving the issue.
- 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.
- 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 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.
- If it's displaying normally on the external monitor that means the built in display is damaged already and replacing it would be the only solution.