The short summary: I have a new build that will only boot with one out of three (known to be good) power supplies. At this point it is starting consistently, but I'm trying to understand the underlying issue and if I should be concerned about the motherboard quitting on me.
I have an ASRock H110 Pro BTC+ motherboard that would not boot: it would power on for a fraction of a second (CPU fan, HDD, case fan would start) then stop. I used 650 watt EVGA and 450 watt Corsair PSUs on the board; both are known to be good. The power switch on the PSU would have to be cycled between attempts to power on, otherwise it would not even start to power on.
I verified all power connections with each PSU. I tried booting with only ATX power supply connected (CPU power disconnected), with and without RAM, with known-good RAM, with all peripherals disconnected (all fans except CPU, monitor, HDD, etc.). With one exception (below) it acted the same in all configurations. I also cleared CMOS between the various configurations.
When I replaced the RAM (8 gb GSkill) with a 4gb stick I know to be good and connected to the 450 watt PSU it booted with nothing connected but ATX and CPU power. When I then connected the monitor, HDD, etc. it went back to powering on for a fraction of a second, then powering off. Even after going back to the bare-bones configuration that had booted, it would no longer boot.
I then tried a 750 watt PSU (that I actually thought was no good, but figured I had nothing to lose) and it booted, with nothing connected. I've since connected everything except the HDD and it has consistently POSTed and I've been able to enter BIOS settings. It also booted with either RAM installed.
Is it possible that the other two power supplies were truly not providing sufficient power to the board, even with nothing but the CPU installed? It just doesn't make any sense to me. Has anyone ever come across an issue like this?