That is worked last week says exactly nothing on the current state of your memory
It's true that this chipset doesn't support 800MHz memory, but in general it should work fine. I've often used 800MHz memory with this chipset and never had a problem. It will just run at 667MHz
I would say either your memory is broken, there is some BIOS option to manually switch this, or there is a problem with the mainboard and/or BIOS.