Windows. Did you try the general Windows 8.1 refresh method? Microsoft notes it at:
Just after the Windows 8.1 update about a year ago, it doesn't work. It constantly goes in a loop with windows logo, then Samsung logo, and some error message. My tech friend managed to fix it somehow (he had no idea) but after a month, it goes in the loop again after booting up. Samsung dealer claim switching to another motherboard would help but I am dubious. Bought the computer with NO WARRANTY.