PC won't boot

So about 3 weeks ago, my pc crashed and when I turned it back on my motherboard flared. I immediately turned it off and unplugged everything from the motherboard. The mothetboard was burned and I bought a new one. Upon arrival of the new one I got everything hooked up and went to turn on my PC. When I hit the power button, the PC runs (all fans turn on and the LED for the power on the front of the case turn on) but my screen on my monitor remains black. I tried switching graphics cards and moving the RAM around and still nothing works. I also put in a brand new processor. At this point I'm losing all hope and any help would be grateful.