Thank you Zhang for your quick response!
I must add that the issue that I couldn't turn off the motherboard was caused by the J1 switch, which was not in its default position. After correcting that, I can turn on and off with the power switch and from IPMI as well.
The other thing I did was to update the BMC firmware from 1.26 to the latest version 1.98 and surprisingly enough, this change is indeed reflected in IPMI.
I have cleared CMOS several times, I also put the J2 switch to BIOS RECOVERY MODE, but so far no luck, I can't get it POST.
Maybe you're right, maybe the board is completely bricked.