Memory is being appropriated

Solution 1:

From your motherboard specifications page:

*When installing total memory of 4GB capacity or more, Windows 32-bit operation system may only recognize less than 3GB. Hence, a total installed memory of less than 3GB is recommended.

This is due, as you have found, to your graphics card and other devices needing to be mapped into the 32-bit (4GiB) address space.

Generally this is only seen with a 32-bit operating system, but if the motherboard is particularly old and badly designed then it can happen with a 64-bit operating system as well.

See my answer to What limits a motherboard from supporting more memory?, as well as other questions such as Why does my sytem only uses 3.2GB of my 4GM RAM?

Basically the first thing to try is running a 64-bit OS, for example a Linux LiveCD such as Ubuntu, to see if that can see the full 4GiB. If it cannot then it is a motherboard issue. If the memory can be seen then you will need to reinstall your current Windows version with a 64-bit version to use the whole 4GiB.