I would firstly test a different power supply. If there's a case speaker (beeper) connected, try starting the board with only CPU and CPU fan installed. See if you get the error beeps signaling memory missing.
Now insert only one RAM stick and see if it does beep signaling no VGA.
I think it's either the power supply or the graphics card.
You can try testing the graphics card in a different PC, just to make sure it does work.