Hi there
Do a test
1) Remove some RAM and see what happens.
2) jiggle around the RAM modules.
3) check in the BIOS that the BIOS actually SEES the full RAM -- windows reads the data from the MOBO - not the BIOS - so while the MOBO might say 4 slots full the BIOS will only allocate say 4GB.
Windows 8.1 is very efficient on RAM usage -- you should get something like mine with 16GB RAM
scr shot below.
Cheers
jimbo
Should there really be compatibility problems? I just bought this pc