hi once more!
can confirm that all the methods provided by you made no difference: clearing CMOS while unplugged does nothing. and when plugging it, fans start spinning, power button LED lights up, and if I plug a USB keyboard it doesn’t light up. as I said, I haven’t been able to test with a different PSU (nothing suitable at hand to try)
the only way to boot it up seems to be to leave it alone and unplugged for some days. if enough time passes it seems to act normally again: it does nothing when plugging the PSU. i can press power up button, it boots up normally and all seems fine.
I tried his morning, afer a few days of inactivity, and I was able to boot it up normally. I checked system/kernel logs but failed to see anything relevant. after some time testing I had to leave, so I left it running. a couple hours later it was again powered on, but without any activity: no video output, no network activity, unable to log remotely….
I want to wait some more days and give it yet another try, keep digging into system logs, etc. But all points to some hardware being broken
I’ll contact afer-sales as you suggest, anyway.
Thanks!