I build a pc and it doesn't work

I have "finished" my build and pc does not work.

Specs: Cpu: Ryzen 5600g box Motherboard: Asus tuf b450m pro gaming RAM: AMD DDR4 16GB 3200MHz Radeon R9 (R9S416G3206U2S) SSD: M.2 500GB Kingston NV1 (SNVS/500G) 550W Gigabyte (P550B)

It's my first build so I have spend 3-4 hours to plug everything. When I pressed "start" button on pc case, everything started - cpu fan, other fans, light on motherboard, and that's all. I plug hdmi monitor - nothing happens, mouse or keyboard into back (motherboard) USB - nothing happens, but if plug flash drive - it has light.

I know that hdmi cable & monitor are fine because it works with my laptop. Pc worked like this for 10-20min, I shut it don't and cpu fan doesn't seem to be any warm - I don't know if must after 20 min of work with cpu that doesn't do anything.

What I think to do next - remove everything from case, and plug cpu, fan, ssd, ram, power, and pins for start button / or just start with touching it with something metal. If I won't succeed, I don't really know what to do next, because I don't know if I missed something, or some part of pc is broken and I need to return all the components to service, and let them find issue (I will do that in few days..)

Do u have any advice for me, how to understand what's wrong and what should I do?