PC keeps rebooting on "cold" start

Hi,

I just put together a system with the following specs:

Motherboard: ASUS M4A785TD-V EVO
CPU: AMD Athlon II X2 250
Memory: G.Skill F3-10600CL9D-4GBNT PC3-10600 DDR3-2GBx2
HDD: Seagate 500GB 7200.12 HDD
Case: Antec NSK4480B-II
BIOS: latest version (M4A785TD-V EVO BIOS 0501)
OS: Windows 7 Ultimate 64 bit.

Now, if i leave the PC off for more than say 6 hours and then turn the PC on again, it would go through the normal boot routine until it boots into Windows. Just after it finishes loading the Antivirus software (or around that time), I would get some memory access related error, the Blue Screen Of Death and then a reboot. It will continue to reboot endlessly (going through a similar boot up routine each time) until I physically switch off the PC using the power button. If I then turn the PC on, it would boot up fine. If I was to reboot (or turn off the PC and turn it on again), it will still be fine. However, it was leave the PC off for more than a few hours, i would get the same symptoms as described above. This is repeatable and happens every time I boot up after leaving the PC off for a period of time. On each time, I would have to physically shut down the PC to end the reboot cycle.

The BSOD error message seems to differ on each reboot. e.g. APC_INDEX_MISMATCH, IRQL_NOT_LESS_OR_EQUAL, PFN_LIST_CORRUPT etc. However, the same set of BSOD error messages seem to appear each time I turn the PC on after a period of shutdown.

I initially left everything in the BIOS at it's default value, except changing the SATA setting from IDE to AHCI for the HDD. The memory settings were left to Auto (Default). I then tried following changes:

1. Set DRAM frequency to 667Mhz, memory timings to 9-9-9-24 and the voltage to 1.5V.
2. Set DRAM frequency to 533Mhz, memory timings to Auto.
3. Set DRAM frequency to 533Mhz, memory timings to 7-7-7-20.

I got the same results (ie. the endless reboots after a few hrs of leaving the PC off) on each of the above 3 settings. I am not able to change the Command Rate. The motherboard sets it to 1T.

I have also tried unplugging the RAM modules from the black slots and plugging them into the blue slots, but am still getting the BSOD (this time a MEMORY_MANAGEMENT error) and reboot after starting up the PC from "cold". Like before the endless reboots would continue until i manually power down the machine using the power switch on the computer case. When i turn the PC on again, it starts up fine. This happens every time after an extended period (6+ hours) of shutdown.

Any idea on what might be causing this? Faulty memory? Faulty motherboard? Faulty power supply? The problem only seems to manifest itself when the PC has been off for several hours.