MacBook display will not boot after logic board clean

About a year ago I had spilled some coffee all over my MacBook and it was left untouched. After booting it up a year later I found that it was running extremely slow and decided to perform an internal clean up.

Once opened up I found a lot of corrosion on the logic board and decided to clean it with Isopropyl 99% alcohol, with a toothbrush, applying minimal pressure. After cleaning the top of the logic board, I proceeded to remove it to inspect the bottom side of it for any signs of corrosion, and whilst I was at it, I replaced the thermal paste on the CPU.

After reassembling the MacBook and reconnecting all the cables to the logic board, I found that upon pressing the power on button the display would no longer boot, it would just be a black screen with no backlight. The fan turns on, and starts spinning excessively fast, and the logic board also feels really hot. The keyboard light does not work, and the caps lock led appears to not be functioning either.

What I think could be the problem: when applying the thermal paste, I think I placed too much on the CPU, and the screws holding down the CPU could have been tightened up too tight. That could explain the temperature but I do not see how that could have possibly affected the display or the keyboard light.

What could have possibly gone wrong here? The MacBook was slow before the cleanup, but at least it booted up, and not it wont boot at all, just powers on without any display.