Hello. Just joined these Forums and I don't know where this thread fits as it could be anything. OK. I don't think this is the Windows 10 'Boot Loop' that I found on google about the subject, as although this happened after clicking on Windows Update (on 8.1) and getting message like 'Preparing Windows 10' or similar it didn't actually install win10. But it did keep shutting down and starting up. No blue screen or message, just as if it was physically being switched on and off with the case button. Because I'm new to self build PC (built a year ago, running fine recently added ASUS STRIX 970, ran fine), I was worried about something shorting and damaging the components and/or Motherboard, so I switched off the power on the PSU rocker switch. When I switched the PSU back on the next day the PC booted straight up without my having to turn it on with the front On/Off button. So my guess is that there is a fault like a short on the power button or something conductive getting in there, and hopefully can (when I get one) put another switch on the header to solve this but as a year young noob I don't want to damage it thinking about electrical shorts elsewhere and the like. The Mobo Light is on and the POST Beep is the normal operation one. Sometimes it happens at the Boot stage and other times Win 8.1 loads up then shuts down after a few minutes(It says 'Shutting Down' and not 'Restarting', returning to the On/Off Cycle. My System: MOBO: ASUS Z87-K, CPU Intel 4th G i5 4460 3.2 GHz, RAM: 8GB DDR3 (4X2), GPU ASUS STRIX GTX 970 4GB (3.5!!!) 1HDD, 650 Watt PSU,. Windows 8.1 (Basic Version) Thanks for reading. I don't know all the lingo as I started a build a year ago from reading and am still learning the basics so apologies in advance. All advice appreciated and I understand if this thread gets moved to an appropriate section if mods see fit.