Why Windows10 64bit sees only 4GB RAM on 8GB installed?

Scenario:

• Windows Home edition 64bit

• RAM: 2x4GB DDR2 800mhz

• Motherboard: Foxcon Q45M (Intel Q45/Q43)(up to 16GB RAM 4x4GB slot)

• CPUZ sees 2x4GB modules

Problem:

The Bios sees 2x4GB = 8GB RAM but Windows sees only 4GB RAM

What I checked (as suggested here: enter link description here) :

1. Turn off Auto RAM Virtualization (done)
2. Check if your RAM is properly seated (done)
3. Check if your RAM is faulty (done)
4. Rearrange your RAM modules (done)

5. Change your BIOS settings:

   • Vitualization – ON.
   • iGPU – OFF.
   • Render Stability – Enabled
   • iGPU memory – Auto

6. Use msconfig (done)

7. Check if your RAM is compatible with your motherboard (done)
8. Check if you have integrated graphics (done)
9. Check if BIOS recognizes your RAM (done)

any tips?thx