Extra RAM not showing up

I have an Asus A555-LF laptop with 4GB integrated RAM(1333 MHz DDR3) (non removable) and an extra RAM expansion slot. I installed another 4GB RAM to the laptop (1333MHz DDR3), but my BIOS, Windows 10 and Ubuntu doesn't detect it. I'm sure I installed it correctly in the computer (prongs are perfectly fitted and connectors lined up).

When I put this RAM on my older laptop, it is detected just fine.

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