If I understand the issue correctly the laptop will not shut down or will just stay on? Here are some troubleshooting steps that may help.
- Start with a hard reboot, unplug it's AC adapter then press and hold the power button for 20 seconds then try booting it.
- If it doesn't work reseat the RAM, remove them all for couple of second then put them back in making sure everything is seated properly.
- Again if these doesn't work but you can hear the laptop on but with no display, connect an external monitor and see if it would display anything because if it does that means it's the built in display that is faulty.
- Next to try is if your AC adapter is still okay by trying another AC adapter that has the same voltage and see if it would work.