Question System open and shut in 1-2 seconds, never get to POSt

[first_time_seb]

Hi,

I'm building a completely new system. Here's what happened :

I got all the part 2 weeks ago. Build everything, get to the BIOS, then the computer shut down in my face. When I started it (after reseting the switch behind the power supply), the computer would just flash the leds (on the cpu) and start spinning the cpu fan before shutting down.

I exchanged the motherboard and cpu's (got a cheaper price because of Black friday), rebuild everything and it's doing the same thing again. The computer turn on for 1-2 seconds than shutdown.

I tried switching the ram around (DDR 4 3200 G. skills for AMD), tried removing the graphic card (Sapphire RX580), the m.2 SSD (Crucial T1). Right now I have an ASUS ROG Strix B450-F Gaming and a Ryzen 7 2700x. I also tried the paper clip test with my PSU (650 watts corsair) and the fan is spinning.

I got a cheap 40$ case, could it be the problem ?

Any other things I should check ?

Thanks all,

 

[first_time_seb]

more info,

took everything out and only plugged mobo on a board, cpu, psu and ram. turn outs it start for 1-2 seconds.

if i do the paper clip test then, the fan only spin 1-2 seconds than shutdowns.... seems to be a problem with the PSU that get "rebooted" if I flipped the switch, but the problem stays when I don't ...

sending PSU back...