Dell Optiplex 7090 MT

When connecting the PSU to AC, or when shutting down Windows, the PC wakes for a few secconds (I see the fans and power button light) and then shut down. It repeats that cycle a few times (Sometime once, sometimes 5 times, sometimes it doesn't do it at all)

I have latest bios version installed.

Made CMOS reset

Replaced power supply

Replaced GPU

Replace RAM

Replaced CPU Thermal paste

Any idea what can cause that?

Thanks!