-5c cannot be a real temp reading. That is below freezing so unless you are running this computer during a winter cold snap outdoors then that is not to be taken seriously. There are many things that can cause instability when overclocking. High temps, CPU voltage too low, NB, HT Link and Ram frequency being too high are among them. We have very little info about your settings at this point. It would be helpful if you would attach pics of CPU-z tabs: CPU, Memory and SPD to your next post. Do you know how to attach pics?