My friend bought a PC that was custom built from a guy on the Facebook Marketplace. Everything ran fine for a while, but now we suspect that the motherboard is in need of replacing. His PC would turn on for a split second and then turn back off. The only time that the PC would remain on is if we unplugged the CPU power connector. We tested this with multiple processors and none of them worked (even the 9700k from my PC that I am typing this on). We diagnosed it to be a short somewhere in the motherboard (we checked for broken pins, and there were none). Unless I am missing something, I think it is time for a new motherboard. However, my friend has been running on an "MSI B360i Pro Gaming ac" motherboard with an i7-7700k. When I look this up, every site says that a combination of a 300 series motherboard with a 7th generation CPU will not work... but it did work for all this time. We also tested his CPU (the i7 7700k) on my MSI z370 motherboard and it posted as well. So my main question is, how could his 7th gen CPU work on both of these forbidden motherboards? We are in the market to buy a new motherboard and would like to know whether he can futureproof his build and get a z370/z390 or does he have to get an older chipset, even though he has been running on a newer one before. Thanks!