In my opinion, there's either a problem with the PSU /power supply unit/ of the motherboard or the motherboard itself. If your laptop is out of warranty, my suggestion is to take the battery out and disconnect the power cable. Then, open the laptop and remove the CMOS battery that lies nexto to the processor. If you have another one, replace it. If not, wait for some minutes to discharge and put it back in. Try to boot the lappy again.