DRED, here is some info for you to easily have. I went to Kingston's site and looked up what you have (if it was from the 1st page).
For Kingston HyperX KHX8500D2K4/4G:
For 1066Mhz:
Latency should be set at 5-5-5-15
Voltage should be set at 2.2V
For 800Mhz:
Latency should be set at 5-5-5-18
Voltage should be set at 1.8V
This is what your RAM runs best at for the given SPD.
Go into BIOS (unfortunately I have ASUS) and adjust both accordingly. You should have NO PROBLEMS after doing so, if you do, revert to 800Mhz (which if I'm understanding the data sheet correctly, is "Default" per se.) But it says it has been tested to 1066Mhz.
My ASUS PK5-E was set at "Auto". I assumed it was at 1066 (I have 2x2GB Mushkins which are PC8500 as well). I was wrong, it was two lines slower on my screen SPD wise. I put it at 1066 and then saved, as the Voltage was already at it's preferred level.
You may already know all of this but, I'm just trying to help. If you need a walk through, PM me your number and I'll be glad to assist you, to the best that I am able.