some times ago (last year) i've cleaned my system with ccleaner, and some days after it started random rebooting at distance of 2-3 days and sometimes after a week. i've spent three months triyng every piece of hardware installed on it but they were all ok. i've got a hint when my 2nd rig got the same issue after using again the same release of ccleaner. so i've restored an image i've done before and everything worked fine again - so i've learned that it's always good to have a recent image stored and to take care when cleaning registry...
anyway, i'm trying to say that it's difficult but random reboots may also be caused by software problems, and if you create an image of your actual installation you won't loose anything. it takes only 10-20 minutes to create an image and another 5 when you decide to restore it.

on the other hand, reading about so many people affected with stability issues at even stock or near stock settings, it's more likely the board is faulty.