You're mixing your 1066MHz CL5 memory with 800MHz CL5 memory.
All four memory modules need to run at the same speed with the same memory timings.
Post a screen-shot of your current setup by following step #4 in EP43-UD3L with Q9400 wont post, keeps rebooting, post #5. Depending on your current overclock settings, you'll probably need to make some bios changes and perform stress testing using Prime95.
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Be sure to include brand names and model numbers.