Ram Speed Issue.

[DSN]

i have 2 racks of :

G.Skill RipJawX 4GB (2x2GB) DDR3 PC3-12800C7 1600MHz Dual Channel Kit (F3-12800CL7D-4GBXM)

8GB total

however as soon as I set my RAM speed to 1600 in my bios

board:
Asus P8P67 DELUXE Intel P67 (Socket 1155) DDR3 Motherboard - (Sandybridge)

the rig fails to boot. and i have to flash the bios to get her back into bios.

All the ram is seated properly. I havent tryed only 2 sticks yet, as its under my noctua and i got a really nice seat onto the cpu

 

[searching]

I built my PC over the weekend and had 2x2gb 1333mhz memory, but looked in the bios (I have P8H67-MPro) and it's clocked it down to 800Mhz for some reason. I also tried changing this to 1333mhz but then windows took ages to load and obviously the memory wasn't working properly. Have read that it may be to do with the timings needing tweaking?