I changed the thermal paste in my computer and now it won't turn on.

I changed the thermal paste in my computer and now it won't turn on.

I changed the thermal paste on my CPU and after reinstalling the motherboard and all cables it won’t boot. All that happens is that my fans turn on for like a second while my start button flashes white. The flash ends and the fans turn off. It keeps going like that until I unplug it. I don’t know if I installed it incorrectly or if I did something else wrong