Ditto on the above advice. If you do check voltages, make sure your system is loaded/stressed while taking the readings. Run Intel Burn Test and Furmark at the same time, and check your voltages then. It is an eye opener with some power supplies.
I admit to being lazy. In situations like this I usually nudge my memory voltage up .1V (assuming you are at 1.5V) and see if that makes a difference. Sometime I will bump my CPU voltage a tad to see if there is any effect. I mainly want to find the weak link. If bumping voltage on either makes a positive difference, then you have a start for the diag. If memory is a problem, run one stick at a time till you find the problem child.
I have no idea how old your system is. GTX 260 was around in the 2008-2009 timeframe, so if it has been used that long, might be a problem. If it is only a couple years old, start looking at memory first.
I am a retired Ford tech. Next to Fords, any computer is a piece of cake. (The cake, its not a lie)
3770K @4.5, Corsair H100, GTX780, 16gig Samsung, Obsidian 700 (yes there is a 700)