Computer will not power on

[puddingoo343]

Hello, i recently bought a new graphics card which in turn made me buy a new psu that was compatible with my graphics card. The problem is that whoever previously built my computer buried cords under the motherboard and I had to take it completely out. Being new to this, i ended up messing with several things including the heatsink, CPU, wireless Wi-Fi card, and some blue cord (which I did plug back in)
After finally removing my old psu, i put the new one in and I believe everything was put in correctly. When I flip the switch to the power, my headphones light up, so I know they are receiving power through the USB port. However, when I press the actual power button, my computer does nothing. I double checked my wires and I'm pretty sure I found a home for everything... I tried everything in the manual to make sure it wasn't a failed PSU and nothing worked. I'm not sure what's wrong with my computer but even though I believe it has power, it wont turn on... does anyone know what the problem is?
Here is what I have:
Gigabyte GeForce GTX 1070 Ti GAMING 8G (GV-N107TGAMING-8GD) https://www.amazon.com/dp/B077P9HX2V?ref=yo_pop_ma_swf

https://www.gigabyte.com/Motherboard/GA-78LMT-USB3-rev-41#ov

Seasonic FOCUS Plus Series SSR-550FX 550W 80+ Gold ATX12V & EPS12V Full Modular 120mm FDB Fan Compact 140 mm Size Power Supply https://www.amazon.com/dp/B073GY89G5?ref=yo_pop_ma_swf

On top of that, i have 24 GB of DDR3 RAM

 

[KR2]

Make sure that your Front-IO connections are in the correct places and that none are missing. If you are unsure what these are, here is an image.
Here is a video as well.

 

[puddingoo343]

Sorry didn't mean to downvote your answer or anything, it's just that I'm new and there's no indicator on how to respond to you. I tried YouTube and nothing helped. I don't have my Motherboard manual but I do have an XPS 630i computer case and I have no idea what cords are which because they aren't labeled as nicely as the ones in that video. As far as I know, i think my Power cord is plugged into my Motherboard, so I believe it is a different issue, but I'm not really sure.

 

[KR2]

You should see some cables coming from where your power button is (inside the case). Those will be your front-IO connections. Usually they're labelled well enough to read..

 

[puddingoo343]

You should see some cables coming from where your power button is (inside the case). Those will be your front-IO connections. Usually they're labelled well enough to read..

Well here's my update: I just tried using a new case, new motherboard, and new psu and my computer refuses to turn on still. I'm honestly stumped. The only thing I can think of now is that I've somehow fried both motherboards. I've already put down so much money on this computer and the costs keep piling...