Regarding your CPU installation I just noticed that you said "The arrow is in the right corner." According to the video I'm linking, it should be in the lower left corner, not right. I understand that you may have meant "correct corner" but I don't want to assume anything. Please check this and verify the CPU is installed in the proper orientation. If it is installed correctly then continue on to the rest of my message.
https://www.youtube.com/watch?v=ymbeMBbbOp8
When a system won't boot for whatever reason that isn't obvious, the first thing you want to do is eliminate all hardware that is absolutely not necessary not necessary to boot - hard drives, SSD's, sound cards, optical drives, etc. The idea is that you want have just the very basic hardware initialize and allow you to get into the UEFI BIOS. If you can do that you are most of the way "home". Once you are into the BIOS you can start swapping out items that might be causing the inability to boot up.
If I was in your situation and you have the heatsink off, I would pull the CPU out and check for bent pins even though the CPU light is green. But that is me, I'd pull the CPU. Possibly this could be overkill but I'd want to eliminate any possibility of an installation error on my part. With the CPU cooler taken off you want to very, very carefully pull out the CPU and check the pins (you will need a magnifying glass) and see if any of them are bent. It is tedious taking out the CPU and checking the pins.
Once the CPU is reinstalled in the socket, clean off the CPU and the heatsink if you haven't already. I use ArctiClean to clean of my CPUs and heatsinks. You can also use the highest purity isopropyl alcohol that you can get at your local drugstore as well. Google "how to clean a cpu heatsink" and you will find a few videos that demonstrate how to do this.
The only items you want installed are the CPU and cooler, one stick of memory in the primary memory slot, and a video card. From a very basic standpoint, the motherboard that you have has integrated video so eliminating an add-on GPU would be preferable but you've already stated that your monitor doesn't have an HDMI port so using onboard video is not a possibility. Since you've gotten a new video card that very probably eliminates video as a source. So, once you get your CPU heatsink reinstalled you want to eliminate the SSD, optical drives, everything else other than cpu, heatsink, one stick of memory and graphics card.
Then reset the CMOS. To reset the CMOS see page 2-20 in the manual (in section 2.2.5). Then try a reboot.
If it doesn't come up then power down and change out the DIMM in the primary DIMM socket with the other one that you have. Reset the CMOS again and try to boot.
At this point if your system won't POST then I'm out of ideas other than to flash the newest BIOS. Lets see what happens if you follow the steps above first before jumping to flash a new BIOS as that process, if done incorrectly, can hose the motherboard although the BIOS flashback system on the new Asus Z77 boards is supposed to be a lot easier and safer to do.