Mobo won't post

Aug 21, 2018
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I just finished building a PC. All of the fans come on (gpu as well) but there is nothing on the screen. I have tried clearing CMOS and trying to boot with one ram stick at a time. No luck so far. When I press the power on button a few seconds later it beeps as normal but nothing.

Specs:
AMD FX6300
Gigabyte GA-990FXA-UD3 rev3.0
Evga GeForce 8800gtx
Patriot G2 Series 2x2gb kit ddr3 1333
2x unifosa 2gb ddr3 1333

I know mixing ram isn't the best, but it's what I've got.