Hello, I have exactly the same problem ! I tried 2x512 MB Corsair, no problem. Then 2x512 MB Kingmax, no problem. Together 4x512 MB and PC can't start, So I used 4x1 GB Samsung and it also didn't work. So I can use only 2 pieces of memorz modules, doesn\t matter of what type or size (tried also combinations of memory modules and it works). But .... All memories are running on 667 MHz, even though they are DDR2-800 and Corsair are Extreme Edition 1066 MHz. As I want to run 2x1 GB I must manually set memory to DDR2-667 MHz.
Can someone help, please ?