“The system has rebooted without cleanly shutting down first. This error could be caused if the system stopped responding, crashed, or lost power unexpectedly.”

This error can be triggered by many different things, but in general they’re all related to something to do with power management.

I just went through three motherboards, different VGA cards and harddisks, basically changing out everything except for the CPU, only to eventually find that the computer crashes were triggered by Windows 7 trying to manage the power state on my Intel Core i5 750 CPU. As soon as I disabled all C-States, it stopped crashing.

I found out about this workaround from the Technet forum threads “Periodic server core BSOD/Reboot, need help with bugcheck report” and “Iam having Microsoft-Windows-Kernel-Power crashes“.

The problem with this workaround, is that the new CPUs are supposed to save you energy by enabling the latest operating systems such as Windows 7 and Server 2008 R2 to manage them more effeciently. By disabling all of the C-States, you’re basically forcing the CPU to run at full steam. This is most severe if you’ve invested in the latest Xeon processors mainly because of these features, as mentioned somewhere further down in the first forum thread I linked to.

If this is a fault with the new Windows core, I really hope Microsoft comes out with a hotfix soon. It cost me a lot of time and frustration to find the source of – and workaround to – the problem.