If the Corsair was the original RAM that was causing freezing, my guess is that it takes 1.65V and your motherboard defaults to provide 1.5V, which would mean it will freeze randomly unless you set the voltage to 1.65V yourself.
Since you added more RAM and are now at 4 sticks, you probably need to bump up the voltage even more because that's one of the weird quirks of using all 4 slots. So to get the Corsair to run right, I'd try 1.7-1.75V. Now, since the G.Skill memory is only at 1.5V, you're going to be oversupplying it. So your options are to either send it back and get something with a voltage that matches your original RAM ... or cross your fingers, jack up the voltage and hope the G.Skill can handle the extra 0.2-0.25V without burning up.
hmmm, very interesting reply, i would never had thought of taking ram voltages into consideration... I will take a look at my BIOS in a short while... I checked the Corsair, it says on the side, 1.60V ver2.2
So I'll see what my default voltage is in the BIOS, and try changing it accordingly... Thanks!