My issue it somewhat similar to this one - Computer continuously power-cycling in terms of symptoms, but different in general.
If I put my computer to sleep manually, or shut it down, it will work fine, but if I let it go to sleep on its own (after however long my timer is set for), it will start, then as soon as the fans power up and start running (2ish seconds) it will abruptly shut off. Then it will do this over and over again.
The only way to stop it, is to unplug the machine, and when I plug it back in, it will start fine, and go back to exactly the same state as it was, as if it was just asleep and not powercycled, which I assume is some feature of windows 8.
If I couldnt boot at all and this was happening, I would suspect it was a mobo problem, but since that's not the case I feel like it may be a PSU issue (i'd heard of problems with low power states of haswell, but i dont have one so...), though really I have no idea.
For information's sake if these matter -
Mobo - GA-Z77X-UD5H ATX LGA1155 Processor - i5 (ivy bridge) PSU - NZXT HALE 90 750W
PS - OH, also. The obvious solution would just be to turn off the sleep setting in windows, but I'd rather not do that, for the times when I forget to, if I can avoid it.
EDIT: When I unplug it, if I immediately plug it back in, it doesnt fix the problem. I have to unplug it for a couple seconds. So That would lead me to believe it has something to do with capacitor type things? Maybe the RAM?