I've been getting the same problem with a P7P55D-EVO. From what I could read online, I've tried to do this two things:
1. Update the BIOS to the latest revisions
2. Set the correct dram voltage
The problem with #2 is the P7P55D setting the default voltage to 1.5V when using the '[Auto]' setting. My RAM is 2x Corsair XMS3 which has a spec of 1.65V. So using the default setting of the motherboard doesn't produce stable result, hence could easily result in the computer freezing.
The step #1 is pretty obvious... when you read the changlog of Asus about the latest BIOS update for this motherboard, you'll notice two of them being release to "improve system stability".