I've tried disconnecting all devices except mobo/cpu/power just to get into bios, but still encountering same issue. PC seemingly won't turn on for more than .1s then turns back off. It is not new, or specific model (custom built) but has been working flawlessly for almost a year until now.
Also the LED on back of case is constantly on meaning there is juice getting to the box. And sometimes hitting power switch has no effect and it wont turn on for even .1s.