Go through with some compressed air and blow out all air vents, heat sinks, and fans. Make sure no dust has collected and is restricting air flow. If there is no dust, you might invest in some higher airflow cooling. Fans can be purchased for your case, though you will need to know what size your case supports (if any). If you need help with that, post your case model and someone will take a look.
Have you run Memtest86 on all the sticks individually yet? If not, go ahead and do so, as it is hard to distinguish between RAM and CPU issues.