The first and easiest thing to try is the power adapter. Does it have a light on it, and if so is it shining?
Ask around and see if you can find someone with a similar HP. If it has a plug which fits your laptop it should be compatible. Take the battery out of yours and try it with their adapter.
If still no joy then it’s not going to be easy. I take it there’s no spash screen, or even a faint glimmer from the screen when you press the power button. And the power button hasn’t lost its click or feels any different to usual. That would indicate there’s a fault in the circuitry close to the power inlet. If you can disassemble it, (see this [guide|126483|disassembly guide] - marked as Diffficult, but it really isn’t) look very carefully for any signs of overheating or burning in that area of the motherboard. If so, take some close-up photos of the area and post another question