I found this, but doesnt work for me yet.
OK, just in case someone has the same problem in future. I left the mini in the hands of a tech guy who couldn't figure it out. But then, someone on Apple discussions pointed out how to solve this issue.
Basically you leave it unplugged for a night, plugged in it, press cmd + alt + p + r along with the power button of the Mac mini.
Now, this might not work right away. If it doesn't work right away, unplugged it from the wall again, leave it for 5 min, then plugged it back in and try it again.
The person who mentioned this said it took 4 days and over 200 tries before it turned back on. For me, it took 2 tries and it worked.
This is also why it happens:
The EFI firmware on the pram has been corrupted and the instruction to start the computer is not being properly executed. EFI firmware is the same as the BIOS on a windows machine
Kuddos to Lemas. All credit goes to that user.
https://superuser.com/questions/1264124/mac-mini-wont-turn-on-after-outage