I've spent an hour in Event Viewer now to find nothing. Really don't know what to look for. But the description that fits the best are event id 41, kernel-power. It describes unexpected shutdown caused by loss of power. But it does not say if its shows a blue screen. What exactly would trigger a blue screen? Every hardware fault?
Event 41, Kernel-Power:
"The system has rebooted without cleanly shutting down first. This error could be caused if the system stopped responding, crashed, or lost power unexpectedly."
I may add that it usually happens at night. I go to sleep with all my windows up and when I sit down the following morning I am welcomed with a nice message saying something like windows has been restored after an unexpected shutdown.