Have the same problem as LordVader.

I recently bought this computer. I got the ASUS P5K mobo with two 866mhz RAM modules (2x1GB).

I ran memtest but it did not indicate any problem at all.

I've got four memory slots. The modules are currently placed in slot 1 and 3.

Will try to switch slots, but i belive it's a compability problem between the mobo and the memory.