I have an Asus P6X58D-E mobo, Intel i7-930, and PX736G2000ELK RAM which have been working reliably for the last 8 months using the XMP settings for DDR3-2000MHz. Suddenly, the system has become unstable at those settings (CPU not overclocked). The only way the system will boot and remain stable is by running the memory at DDR3-1066MHz. I've tried everything in between and the system is unstable (1333, 1600, 1866, etc.).

Cooling is very adequate. The system is installed in an Antec P180 case with 2 full size fans in the front sucking in, 2 fans in the back exhausting up and out, and 2 full size fans mounted on a Hyper 212 cooler in push/pull configuration to cool the CPU. The RAM itself has heatsinks installed.

Any ideas on this specific combination and how I might be able to resolve it? Asus mobo BIOS is 0701. Cheers.