Hello, I have a problem with ONDA B250-D8P

i have all plug :

- Intel Celeron G3930
- sodimm 4 GB 1333 MHz 1.35 V RAM
- all connected connectors molex ...


Start bouton and :

black screen nothing hdmi video output signal on my screen. Can not access bios. However usb lights and keyboard off.

how to treat hdmi display activation with no bios acces ?