Starting up with new computer

Hello!

I’ve got a question/problem…
I have just bought a new Mainboard, CPU and Grafic card.

I have tried it so long until the PC can power up. But the problem is, the monitor didn’t power up,so I can’t see anything. I have put the cable into the graficcard.

Is there someting that I have to change on the mainboard?

Please, Can anyone give my some advices? I need it really.

Thanks very much!
Regards,
Peg