I am a new member but I think I will become quite active, I love this site.
I am having the same exact issue... no BSOD, XCom went black and rebooted. XCom (installed through Steam) reboots my PC. This is an Origin PC system, brand new with Nvidia cards running in SLI. My system has done this twice, the first time the BIOS (ASUS) was running in Normal Mode, the Second One in power saving mode. I have been scourging the network and I can see many XCom users having the same issue since Windows 8.1 (I am running Win 10), but the developers at 2K games blame the hardware most of the time. I don't think my PC is the problem since I run newer and more "power consuming" and "graphics demanding" games and only XCom does this to me. Anyways, I am sharing my sopecs and toolbox report with you just for sanity.
Mod Edit: Split from http://www.bleepingcomputer.com/forums/t/569433/computer-shuts-off-and-restarts-when-playing-game/page-0 - Hamluis.
Edited by hamluis, 13 September 2015 - 05:44 PM.