You may want to try overclocking from the BIOS default or "fail safe settings." Load them and enter the BIOS on re-start to make your adjustments - some BIOSes hold the settings it made for the settings you left on AUTO from your last OC. You may also want to run memtest86+ for each of your OC attempts. Try setting the FSB at 400MHz, set the RAM timings and RAM voltage to the settings on the RAM stickers, and adjust the MEM srtap/divider so your RAM are running at 1066MHz. Save and exit the BIOS, POST, and boot to memtest.