So, after some troubleshooting, I finally reached the light out of the tunnel.

And the solution was so easy that I felt ashamed.
Thank you all for your precious help.
I will for sure bother you again while on my learning curve
EDIT: I forgot to ask: Does this mean that the RAM module is defective and I have to replace it?
And the solution was so easy that I felt ashamed.
- This is my first double CPU MB. I usually connect only the 24-pin cable from the PSU to the MB. But this MB has also two 8-pin power supply connectors. Once connected to the PSU, I had no more issues in booting or with the FANs.
- Sensors. I'm quoting a statement found on the web
the IPMI sensors never worked while the computer sat in BIOS Setup; they did work when booted to FreeDOS on a USB flash drive. Several of the Supermicro FAQs address this issue: only 1 program / service can directly monitor the hardware sensors at a time.)
Thank you all for your precious help.
I will for sure bother you again while on my learning curve
EDIT: I forgot to ask: Does this mean that the RAM module is defective and I have to replace it?