No Boot After Thermal Paste Reallication

After taking apart my 16-inch for the first time and applying new thermal paste, the computer will no longer boot. I see the backlight turn on, but only to a black screen. then i hear a burst of fan noise and the system powers off. It will then power cycle like this until i hold the power button down. I have now attempted to reassemble the mac a second time worried that I missed a cable… and I’ve reseated the cables four times….

Is there some sort of secret step after taking these new Macs apart that I’m unaware of?