Recently, a Windows 7 PC was experiencing reboots right in the middle, no warning, no errors. A large CAD package with its own built-in Explorer analogue was kept running all the time. I finally turned off Offline Files on the PC: under 7, it turns out that offline files is default turned on for everyone, and every five minutes it checks to see if the network has become slow. Apparently this detection is faulty, and not only is it faulty, but it can conflict with a file explorer subsystem badly enough to cause a system reboot!