x64 Windows reports 32GB RAM usable out of 64GB RAM installed - why?
Most likely a licensing problem. As an example, the Standard Edition of Server 2003 64bit can use only 32GB of RAM, not for technical but licensing reasons.
What Edition do you run?
Figured it out - the guys who supplied the server installed Windows Server 2008 R2 Standard edition on it, which only supports up to 32GB of RAM
http://msdn.microsoft.com/en-us/library/aa366778%28VS.85%29.aspx