HP G42 Laptot won't start, has starting problem

My HP G42-456TU Laptop with Intel Core i3 processor has starting problem. When prower button pressed, Power LED & Fan start for 2 second .

Laptop won't start.

In switch off mode KB3926 got heated and USB port (+V ) 5volts always availabe ,this is unusual .

I have replaced KB3926 I/O chip...

Now KB3926 is normal and USB port is normal but Laptop Won't start, only Power Led & Fan start for 2 second.

Please help me.