ram not detected in slot 2 - 4 Ways to Check Your Installed RAM and Available RAM Slots on ... winner 888 slot

I have 2 RAM slots on my laptop. 1st slot already has a 4gb single-channel RAM. I want to put another 4gb RAM stick in 2nd slot.

Not stopping there, because our PC has dual-channel RAM (most people plug in 2 sticks and either slots 1 3 or 2 4) so we have to multiply by 2, giving us. 25 ...

So after shutdown (power switch on PSU is still ON) once again I tried with slot PCIE_E3, it worked but if I turn off PSU after shutdown (cold start) it's not detected in BIOS Bios motherboard explorer still shows PCIE_E2 is populated.