I'm running Windows 8.1 on an HP DX5150 (small form factor), AMD Athlon 4400 2.20Ghz. I have four 1GB sticks of DDR RAM installed, but Windows says that only 3.06GB is "available" (although it says 4.00GB is installed).
I've swapped out each of the 1GB sticks with a 512MB stick (so 3.50GB installed), and have switched around which DIMM I put each stick in to, but still Windows says 3.06GB is available. BIOS says 4GB RAM (and 3.5GB RAM when the 512MB stick is switched in), so BIOS is reading it.
I've run Memtest86, which only recognizes 3.06GB; Memtest86 says no errors on the 3.06GB, so it's not really helpful. Msconfig advanced boot options does not have 'max memory' enabled so there is no Windows-set cap. And I've enabled memory remapping.
Any ideas of what the problem is?