What your descries above like your forgot to plug in your ATX 4-pin 12V (it can be 8-pin for 2 line of 12V, depend on your motheboard) supply for CPU, which regular palace near CPU socket.

Both CPU and PSU are fine, but forgot that 12V cause system run up for few second before auto power down (it can automatically start up again and then down, and so on)

update: Your motherboard is 4-pin, locate at I on page 11 of your motherboard manual

What you describe makes it seem like you forgot to plug in your ATX 4-pin 12V supply (it can be 8-pin for 2 lines of 12V, depending on your motherboard) for the CPU. The socket for this is usually placed near the CPU socket.

Both CPU and PSU are fine, but not having that 12V supply will cause the system run up for few second and then auto power down (it can automatically start up again and then down, and so on)

Update: Your motherboard has a 4-pin socket, located at "I" on page 11 of your motherboard manual.

What your descries above like your forgot to plug in your ATX 4-pin 12V (it can be 8-pin for 2 line of 12V, depend on your motheboard) supply for CPU, which regular palace near CPU socket.

Both CPU and PSU are fine, but forgot that 12V cause system run up for few second before auto power down (it can automatically start up again and then down, and so on)

What your descries above like your forgot to plug in your ATX 4-pin 12V (it can be 8-pin for 2 line of 12V, depend on your motheboard) supply for CPU, which regular palace near CPU socket.

Both CPU and PSU are fine, but forgot that 12V cause system run up for few second before auto power down (it can automatically start up again and then down, and so on)

update: Your motherboard is 4-pin, locate at I on page 11 of your motherboard manual