So. I was just browsing the web and listening to WMP without any heavy if any at all tasks in the background when my PC just shut down as if there was a power outage, except it wasn't one because I have a TV running in the same room with me right now. As "shut down" I mean sudden power loss and blank screen rather than the nice and warm Windows' shutdown. 2s after that it just booted up again as if it had randomly decided to just spook me by restarting. So motherboard splash shows up, Windows loads and just at the moment when the Windows' logon screen is supposed to show it shuts down again. This time it doesn't boot up again by itself, in fact, it doesn't boot up at all - even when pressing the power button. I flipped the PSU's power switch to off and then again to on and wiggled the PSU cord, then the PC could be booted up and all went smooth and now I'm writing this.
I built this whole PC fresh ~5 months ago. I have a Corsair RM650 PSU, i5-4670k non-OCed (it's a waste, I know), MSI Z97-G45, WD 1TB blue, 2xCrucial Tracers 4GB @ 1886 MHz (at which they're also rated). I think those are the parts that matter here, and it probably isn't an overheat because, as I said, I was on minimal load and the PC was on for only 2h. I also have 4x140mm and 2x120mm Corsair fans rigged in a balanced configuration, though I'm living on my stock CPU cooler.
This is probably pointless but I just want to diagnose early if there's a problem. So, is there one? Or is just a phase?