You didn't mention your PSU, maybe the 12th card was too much for it.
Sticking with a stable 11 card rig is good advice.
i have 2x 1000w corsair so my 10 cars used around 1100w. my plan is 14gpus for this rig.
very few if anyone has a working 14 card windows 10 rig.
let us know if you ever get there as I am interested in it.