TVeblen, thanks for your input.
Yeah I know about the integrated memory controller with the new cpu's. That's what had me worried at first.
I did a search about CPR and it seems to be a feature of Asus boards only?? Anyway, yes I always load defaults before and after flashing. But on this build I've been running it stock since I haven't got round to buying a decent HSF yet.
So it wasn't a problem with any oc setting or anything like that.
It's still puzzling me why this happened. The system has been running perfectly stable for the past couple of days though, knock on wood.