monitor and keyboard inactive, what happens?

I have a problem with my PC:
When I lighter, it starts but nothing on the screen (black) and inactive keyboard.
I rebooted, nothing new
Tested the screen with another PC, it is OK

You should try to make a "clear CMOS" on your motherboard. Specifically, you can do this in two ways:

1) Move the little adequate jumper on the motherboard

2) Remove the battery from the motherboard for 1 / 4 hour before the place.

My keyboard remains lit even when the PC is switched off and this is normal since the motherboard is still powered. The same goes for USB devices.

On the keyboard inactive, there is no LED above?

For the display, should be able to try another graphics card. Any that is the same standard (AGP, PCI, PCI Express) appropriate.