This problem occurred sometime between the time I upgraded from 64bit vista, to windows 7 ultimate 64bit, and updated my bios.
Initially windows showed 6gb with 4gb usable, and during POST it only showed 4gb. I tried turning on memory remapping and nothing happened, I found out my mobo's manual was written incorrectly, so I rearranged my ram from single channel to triple channel. Once I did that BIOS reports 6gb, and windows allows .5gb more usable now (up to 4.5). I've gone into msconfig and changed maximum memory, turned it on... turned it off, tried changing the values, and still nothing changed.
Anyone else have any other ideas? All voltages are still completely stock.
Ok, scratch that. Solved? Some how a combination of me rearranging my ram to triple channel and toggling maximum memory in msconfig solved the problem? I really have no idea what worked, but somehow it's fixed.