I've just upgraded my memory to dual channel 2X 1GB corsair 400mhz sticks in the blue slots. It boots fine no problem whatsoever, but when I try to use the old 512MB in the other slot it hangs and just continouse beeps without posting.? Ive tried it both in slot 2& 4. On its own both 512MB sticks worked fine. with just 3 in it beeps