4GB RAM Installed, 2GB Usable

I've had this problem for quite some time, and the fact it's bugging me already because it felt like I'm running a 1GB RAM Windows 7 all over again made me want to solve this problem already.

A few months ago, my graphics card was removed because I thought it was dead. (Only got it fixed by the old-school style of eraser) A few days later, I noticed that my computer is starting to get slower, so I checked my PC info and realized that only half of the memory was usable and the remaining was on Hardware Reserved. So I searched online for solutions and none of them worked.

I tried several things to get my Memory checked, here are the results:
BIOS: 2 GB
- Frequency read "667MHz (half of that is one RAM stick), Single-Channel"
Windows: 4GB (2GB usable)
- Tried looking at Windows 8 64-bit, 32-bit and Windows 7 32-bit. Same result.
Linux: 2GB
Speccy: 2GB
CPU-Z: 2GB

Specs:

OS: Windows 8 Professional 64-bit
Motherboard: ECS A740GM-M v7.0
CPU: AMD Athlon II X3 440
Graphics: ATI Radeon HD 4600 Series (4650 specifically)

Solutions I tried:
- msconfig, unchecked the Maximum Memory.
- Lowering the Memory Voltage to 1.8V (returned back to 1.85V afterwards)
- Exchanging the RAM sticks' slots.*
- Windows Memory Diagnostic tool, no errors reported (If I remember correctly, only 1 RAM stick was detected)

* - As far as my memory can tell, the result was the same; 2GB usable.

As I installed and checked my specs on Speccy and CPU-Z, only Slot 1 was read while Slot 2 was not detected at all.

My RAM was bought in pairs, same thing, so it could not be mismatch problem. I also tried removing Slot 1 (Unintentionally. Because I couldn't figure out which one was Slot 1 or Slot 2 that time. And I was blind enough to miss that they were identified in the motherboard in white letters) and CPU-Z was able to read Slot 2, so faulty memory is kind of out of the picture.

If there's anything I need to tell about my specs, please go ahead.

Any help is appreciated, thank you.