You have received very good trouble shooting advice already.
Have you tried any of them?
Please confirm what steps you have done and specify the ones you have not done.
Cold boot issues can be caused by software, drivers, settings and/or hardware.
This is a difficult problem to troubleshoot, it's similar to an intermittent electrical fault, it may take several tests run repeatedly to find the cause.
If you're having the same or worse issues with the Beta BIOS I would recommend to go back to the last stable BIOS.
Beta BIOS are sometimes not full versions and may add other instability issues to your current problems.
A good place to start is to follow all the steps suggested by Greg in post #2. Also Carl's BSOD log files, he can analyze them while you're testing hardware.
For the Memtest86+ tests I would follow this tutorial:
Be sure to follow the steps in Part 3, this will test the RAM cards and the motherboard slots.
It is possible for all three RAM cards to pass, then when run with one card it can fail. Number of RAM cards assuming 3x2GB.
It is also possible that it will pass several times and then fail.
You should also run memtest86+ under cold boot conditions. Run it from USB memory stick if possible, or from CD, at first startup. This can eliminate the possible settings and/or software probable causes.
There definitely are several possible causes but, have seen this resolved by adjusting RAM settings or running new RAM, by either testing with different RAM cards or RMA'ing the RAM.
Again, suggest you start from Greg's post #2, and Carl's post #10.
Can you download CPUZ and post a snip of the CPU, Mainboard, Memory, and SPD tabs.
This will give us some information on your system and hopefully some clues for us to continue.
For posting the information , enter 'Snipping tool' in the Start button > Search box, hit enter. Select the area you want to post and save to a convenient place.
How to Post a Screenshot in Seven Forums
Have you been checking your temperatures?
Use Speed Fan or Real Temp , run one of these and check the CPU temps when at idle, under load and/or testing.
Let us know the minimum and maximum temps you get.
Let us know the progress.
If you're methodical and let us know the results from each step, this will help us to resolve your issues.