Blank monitor

Hello,
I have a HP Pavilion a1712n and every time I turn on the computer, nothing shows up on the screen. Interesting enough, when it turns on, the fan starts running and I hear no noise, but the lights do not come up. Only the little green light in the cd drive. I took out the power supply it had tried one with more watts. Even then the lights still didn't come on or the screen. I tried monitors i knew worked and it still never came on. I tried to use a PCI video card, and attactched it on the motherboard because I thought maybe the on board graphics were bad but that still didn't work. I don't know what else to try