I had one irritating issue with my DS3 in that 2 sticks of RAM was fine, but 4 was not.
I went with 2x512MB then upped to 4x512MB and then I had issues.
I went with 2x1GB and it was fine and then 4x1GB and issues again.
Now, on this note, I will confess that it was ONLY with the GEIL ram, the corsair was fine and when I shuffled the sticks to make doubly sure they were seated correctly and they were perfect after that.
Also I had to nudge the voltage up a notch too... The first BIOS I had, I had to use the corsair to get into the BIOS to set the Voltages and then slap the geil in afterwards, but from about F7 it ran the RAM fine as-is.
Maybe upping the BIOS might bring some luck too? - I think its F13 now?
So, thats my choices...
1 - Seating arrangement
2 - Voltage
3 - BIOS