Why Do I have Memory Problems?

I have continual issues with memory. I have 64 GB of RAM with a 2.60 GHz PC running on Win7 Pro. I have up to 12 corridors that are all under 4MB. The terrain is 100MB to 200MB.

I get shut down every 30 minutes or so with memory errors. I have only essential applications running on the system.

Are there any settings that I can check to improve the issue?