If you use only the 800mhz ram and there is no display, then the motherboard does not support 800mhz ram. If you mix and it works, then there is a possibility the rams are running with the lower 667mhz ones. But the biggest problem you should realize is this. One of the rams will fail. I have seen this many times since PC100/133 days. Even some DDR266/400 matchings can cause either one to fail. I remember it was caused by voltage issue, even though there is no overclocking. The symptoms are overheating ram cards.