PC build complete, but can't figure out why it won't power on correctly?

Oct 13, 2018
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Here is the part list. When the build was complete and plugged it in, everything seemed normal. Lights came on, fans were working, but nothing ever appeared on the monitor which was connected via HDMI (I tried plugging HDMI into the mobo and the graphics card). I then realized I forgot to plug in the 4-pronged PCI power in from the mobo to the PSU, so I did, but then when I tried to power it on I just saw a tiny LED flash on the mobo and nothing else worked.

https://imgur.com/a/TJV4BTP