Question Chrsitmas new build not working after working once!

[Anyonehelpme]

Me and my Son decided to build a gaming pc for his Christmas pressie.....
RoG B5550 f motherboard
Ryzen 5 5600 X
Sapphire Radeon RX6500 XT Pulse
2 x8gb ram - Team group Vulcan
RPG 500W power supply
CiT GForce Mid-TOwer ATX RGB PC Gaming Case

So I carefully put the PC together (never built one but am pretty familiar with computers in general).
Started her up, lights on fans on pc case all on and working, installed a fresh copy of windows and did some general driver updates. Shut the pc down unplugged from wall.
Next day - NOTHING - if I press the power button the fan RGB lights on case clink red once and the fans try to start spinning (unsuccessfully) - it's like a different PC - a dead one 🙁
Any advice??? We were so excited everything was up and running and now nothing?
P.s. computer wasn't moved at all

 

[rgd1101]

test with a different psu?

 

[Anyonehelpme]

test with a different psu?

Tested PSU with paperclip method and seems to be working