You reinstalled Windows, right? Upon installation, Windows writes hardware-specific data into a Hardware Abstraction Layer (HAL) which is specific for the hardware it sees at installation. If you change the MB (to a different model), you'll need to at least do a "repair install" of Windows.

How did you switch into single channel mode? Or did you change the DIMM config by inserting/removing/moving a stick? If the latter, does the error correlate with any specific slot in use or not in use, or with a specific DIMM?

What model number power supply do you have?
Are you overclocking?

How were they set before? "Auto" (e.g. SPD) mode?

did you check the stress.txt?
have you tried with a different graphics card?
i had issues where my PC would crash and i'd have to restart, or it'd just restart when it had heavy workload, during games and stuff like video encoding.
found out later when i tried a different grfx card what was wrong.
btw, try running memtest on each stick indevidually, and try changing the slots the RAM runs in.

Try leaving the bios set to SPD/Auto detect but with the manually raised voltage.

After you updated the bios did you also clear CMOS? That should be done. Enter the bios hardware/health page and note the temperatures and voltages displayed. If you have a multimeter check the PSU voltage more directly.

Run Memtest86+ for several hours. First in dual channel mode, stopping the test if it has any errors. If there are no errors let it run several hours, preferribly overnight.

If there are errors, you are saying that just changing from dual channel to single channel mode, meaning you do not remove any memory nor change bios settings, results in regaining stability? I mean in Memtest86+, let's isolate the memory subsystem instead of throwing CPU loading into the mix as is done with Prime95 and by the way, when testing a dual core CPU you should use Orthos to load both cores.

OCZ has a forum where you can post your system specs, the info on specific modules and be advised, whether they know of an incompatibility or what they will do to replace your memory if necessary. If you still have the option of returning the memory to the seller and getting money back, that can also be worthwhile to consider because if it is an incompatibility between the memory and motherboard you may not have a resolution by only replacing two otherwise ok modules with the same exact thing. If that were the situation you'd be better off with the money to buy something else.