I know how frustrating it is not getting anything on the screen, because I've had that happen to me numerous... times [I can't even count]. I'm assuming it's your video card. Try a PCI video card from another comp or something see if that works. Because recently I had a video card that just wouldn't work with my mainboard [Asus]. I don't know and hope that's not the situation for you, because I ended up having to buy a new board [MSI].
See if you can get it working on some other videocard and then go into device manager and see what the problem is....
Also check to see that everything is plugged in right, especially the cpu, make sure it's not overheating or whatever... that you got a good amount of heat paste put on. Also be very careful when putting this stuff together... you never know when you've broken something.
Best of luck.
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