The obvious conclusion was also recognised by others about a new board seeing bad capacitors explaining why it failed to start up on the 4th day of use. The old case had to be put back into use while waiting for the RMA on the new board and it'e replacement. Hopefully it wasn't part of a bad batch of boards were the 2nd and even 3rd like seen with a friend's new build some time back saw.
The thing to note is that there simply are times when you may get a bad board when wotking on a new build. While it can be frustrating having the old case still onhand while waiting to see how things work out on any new build can save the day. At least it keeps you going while waiting.
It's being picked up for return rma very soon like wednedays morning. The request for a parcel pickup was delayed by the Labor Day holiday here. You can bet that something like a cap went after only the few days of seeing it run and poof! press power to see fans spins for those few seconds.
On a friend's build last year I still have to wonder if those first 3 boards sent to him were actually bad or were seeing what I saw when swapping supplies recently. On the 939 build here I simply unplugged the 12v cpy feed and replugged it back in very lightly to suddenly see the system come to life. The difference there to note was nothind was seen while the new build saw 3 full days of life.
Bad caps is nothing new for a long list of electronic devices going back to the old cd radio days where you would sometimes see a new until fail then. You can look at just about any consumer electronics device and see caps since they are about the most common component used.