Chances are it may just have hibernated or worst case it your OS got corrupted. 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.
- 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 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.