Something may be shorting the motherboard or a setting in the BIOS may have become corrupted.
Try disconnecting, taking out the battery and discharging all power in system by holding down power button for 30 seconds.
Reset the CMOS by disconnecting the coin battery.
''The round, coin sized, black covered object with 2 wires (black and red) running to motherboard connector to the right under the main battery''. Video may help:
https://www.youtube.com/watch?v=-UIPoU-8CQQ
This will set all settings in the BIOS to factory defaults.
Also disconnect the hard drive and Wi-Fi in case one of these is causing the problem.