8.0 GB RAM installed, 3.97 GB usable.

I have exactly the same thing. 8GB installed and only 3.98GB usable.

The "Memory Mapping" is "Enabled" in the bios settings, and in the BOOT Advanced options the "Maximum Memory" box is Unchecked.   I even tried setting it at 8192 but still only 3.98GB usable?

Same issues ,BUT found you need to install A M Ds newest driver for video card and or A P U if necessary ; run memory diagnostic as I found 2 out of 4 memory cards were damaged ; after issues with corrupt runtime-broker in win8 system as I had 16gb ddr3(4x4gb) now have 8gb ddr3(2x4gb) and runs better on 2.7ghz A M D 3400 A P U as only video on a 200 watt power supply with 4 sata hdd's and with usb hdtv for Windows Media Center. Set standard bios ,do not tweak until Microsoft fixes win8.1 s problems as I think these issues burned out my memory somewhat(and(2x4gb) 8gb ddr3 ain't cheap either!)Clear IE10-IE11 caches with registry cleaner, this helps too....         ***check bios memory setting for memory ,is it 1333,1600,or 1800 just make sure its set to original (manufacturers setting) ,not higher motherboard tweaked setting!!!

Edwindwight,

Interesting , I wonder if each stick of memory is same version number(as this was my memory issue as the older was best , and new was causing crashes-or was shipped as damaged) and try to put both memory sticks in same color slots ;try black then blue ..FIRST put memory sticks in a plastic-wax grocery bag or anti-static bag before replacing them on motherboard(For just a minute or so) . It's either the memory or ATI graphics effecting the hardware recognition. IF Possible contact motherboard manufacturer for support as  a s u s helped me repair my issues as I was totally frustrated getting PC ran into problem errors all the time ; Now runs like a Ferrari , not a vw bug :} If all fails get an A S U S board , they're always reliable and support is great too. ASUS fm1 CSM Motherboard ,                                         dual core AMDRadeon6410APU-CPU , 2x4gb ddr3 1600 XMS Corsair  ***upgrades for future if needed with CPU , Memory ,Self built in Jan2013, under 200.00.