Well, not much advice to give without knowing what your hardware is. I can't say if it's 1066 RAM functioning properly or 1333/1600 RAM not without knowing that. Buying hardware without actually finding out what you're buying makes these kind of diagnoses tricky! Hopefully you didn't pay very much.
I had same problem with my old pc setup , its most likely your ddr isnt beeing pushed to its limits trugh bios , chek what it shows there if needed manualy stup into fiding the one with your specs , hope it helps