Re: Full usage of RAM
Can you go to Control Panel, then System and Security, then System, and double-check that the Operating System is 64-bit? Under your system specifications, "System Type x64-based PC" leads me to think that your operating system is indeed 64-bit. However, that may be merely talking about CPU support. 64-bit systems should allow up to 196GB of RAM (depending on the Windows 7 version; Home Premium is 16GB). The only logical reason for the system to only recognize 3.96GB would be that it is a 32-bit OS.
Also, can you tell me exactly where you read this information? Can you hit Ctrl + Shift (left) + Esc, click on the "Performance" tab, and read us the "Total Physical Memory" value. It should be a 4-digit number in (MB). If this number is 6xxx, then your system is reading all of the memory installed; it just happens that you're currently using 2GB and you have 4GB left. In any case, 4GB is more than enough for gaming.