GA-EP45-UD3P Max-4GB Ram?

I've got a GA-EP45-UD3P that has been running perfectly non-OC for several months with 8GB Ram. Suddenly, I begin to experience weird hangs and then trouble rebooting. I suspect my Vista install is corrupted, so I reinstall from a backup, but no luck. I try rebooting on a live CD ((Hawk-PE) to run mem tests and it hangs on testing or gives mem errors. I remove two of the four sticks of Corsair CM2X2048-6400C5 (5-5-5-18 800MHz) RAM and it works fine. I try putting back two and removing the first two, and it still tests fine. I try the first two in the slots for the second two and vice-a-versa, and it all tests fine. I put back all four sticks and it immediately fails. It may refuse to boot, or hang on the memtest or have memtest errors with 8GB of RAM. I've also seen reboot loops.

Any suggestions for me?

I have some other RAM (but only 2 1GB sticks), and I could adjust mem timing or voltage settings, but I'd appreciate some suggestions on where to go from here.
Thanks in advance!

Thanks for the suggestion - I'll try bumping the voltages. Do you want to recommend another brand of RAM for me to try?

Two things:

1. Run Memtest (or try) on a single stick at at time. See your motherboard manual for the slot to use.

2. No current game will run any differently with 8GB then 4GB. It's unlikely that you could ever notice a speedup with more than 4GB multitasking either.

Always welcome! If it still refuses to work, post back - we can 'fiddle' a little more with the settings; if MemTest86+ says the sticks are good, it's pretty certain to be gotten to work, one way or another...