First thing - download a copy of MemTest86+:
http://www.memtest.org/download/4.00/memtest86+-4.00.is...
and burn the iso to a CD to make a bootable RAM tester that will comprehensively test
all of your RAM...
If you haven't yet done it, start with a BIOS' "Load Optimized Defaults"...
On the "MB Intelligent Tweaker(M.I.T.)" page:
"Robust Graphics Booster" to "Auto"
"PCI Express Frequency (Mhz)" to "100" (not auto...)
"C.I.A.2" to "Disabled"
******** DRAM Performance Control ********
"Performance Enhance" to "Standard"
Check that the RAM itself was set to 2.1V by the load optimized; if not, do so manually, by:
"System Voltage Control" to "Manual"
"DDR2 OverVoltage Control" to "+0.3"
<F10> to save & reboot...
Boot to MemTest disk, run at least a full pass...
If successful, try booting to OS...
If problems, take out one stick, test the remaining one; if error, likely bad stick; else - exchange sticks & test other one - should point out the culprit...