Question PC wont boot. PLEASE HELP

[HardNotes]

My pc won't boot at all when I push the power button a small fash of RGB appears and fans spin for a second before stopping, They are all brand new parts if you have any knowledge on what is happening please respond.
PSU; Cooler Master MWE Gold 650
Motherboard; Gigabyte B450 S2H

 

[HardNotes]

I should mention that before I had forgotten to plug in the case fans and the RGB for the case fans, there was no issue of this sort before the case fans would not spin because they were not plugged in but the CPU fan spun like normal

 

[kurdtnz]

Please list full system specs, including cpu,gpu etc.

 

[HardNotes]

MOTHERBOARD; B450 S2H
GPU; EVGA GTX 1660
CPU; RYZEN 5 2600
RAM; HYPERX FURY 8GB
SSD; WESTERN DIGITAL BLUE 1TB M.2
PSU; MWE GOLD 650 MODULAR

 

[HardNotes]

I have thought I have found the root of this problem but I don't know how to fix it, whenever I plug the GPU the system fails to post but when there is no GPU it works fine all fans spin and works like normal