Does it still show the Lenovo splash screen? Please do try these troubleshooting steps that may help.
- Do a hard reboot first, remove the battery and unplug its AC adapter then press and hold the power button for 20 seconds then try booting it up again.
- If you can hear the laptop on but there's no display connect an external display and check if you'll get a display from it because if you do that means the problem is the built in display.
- What you can do is to check the ribbon cable that connects the LCD to the motherboard.
- But is you won't see anything on the external display continue with reseating the RAM's, remove them all for couple of seconds then put them back in making sure everything is seated properly.
- If these will not work as well test your AC adapter or try a different AC adapter that has the same voltage and see if it will boot up normally.
- If all these will not work the problem would be the motherboard itself.