Win7 Ultimate x64 reboots while idle after 16 minutes

[Deathinmusic]

I have a weird problem where my Windows 7 reboots after being idle for 16 minutes and a few seconds. It's always at the same point, I have timed it a few times. There is no BSOD, it just reboots like someone pressing the reset button of the computer. However, if I uncheck the "automatically restart" from advanced system settings (startup and recovery page), then it won't reboot but just freezes the computer with a black screen, at which point I have to either reset or turn off the machine. It also does this even if I leave something like utorrent running in the background with active torrents but not for example if I have a video running in MPC-HC x64.

I haven't installed any new hardware recently and I don't know how the problem appeared but this Windows installation used to work perfectly before. I am at a loss and would really appreciate some help.

Here is what I have tried so far which has had no effect:
- Tweaked power options (sleep disabled/enabled, turn off display disabled/enabled etc.)
- Updated to the latest UEFI firmware of my motherboard
- Ran memtest86+, passed with no errors
- Ran a full virus scan, all clean

 

[DeanP]

Hello and welcome to Seven Forums,

Please read this thread: http://www.sevenforums.com/tutorials/681-startup-repair.html

Regards,
Dean