Hp G62 Does not boot and with blank screen

Hello,

I was using my laptop last year connected directly to the AC supplier without its battery and someone happened to pull out the charger and the laptop went black. After the incident, it switched on but did not boot. It displayed a behind-lit black screen.....i formatted the hard drive several times and installed a new windows OS but the problem still remains the same. Everything is running except for the booting and if i use the hard drive as an external drive, it fully works with no problems. How do i resolve the problem??

Thanks