Question RAM slot has stopped working ?

[DescL]

Hello everyone,
My dad complained about a slow computer.
Having only 4gb of ram, I suggested buying another stick of 4gb and switching to SSD.
He bought other stick (same speed, same voltage) and I inserted it.
Computer turned on fine showing 8gb ram.
After reinstalling the cover, laptop did not want to turn on again.
I tested by removing and switching the ram sticks around, both sticks work but only in 1 slot (the slot always used until now).
The new slot refuses to accept the working ram despite working before. All pins seem okay, nothing bend of out of the ordinary. I blew over the pins to remove any dust if that was the problem. Nothing changed.

Did I miss something of what might be the reason the slot stopped working?
Thank you for your suggestions.

 

[Lutfij]

Welcome to the forums, newcomer!

Are the 2x4GB sticks of ram the same make and model? If not, please parse images or links to the sticks of ram used. You can use CPU-Z to show you the ram's specifications(and the laptop's BIOS version). Make and model of your dad's laptop? An SKU will help us two fold. As a side note, you're advised to make sure you're on the latest BIOS version before performing any hardware upgrades. If your laptop has a number of BIOS versions pending update, do not jump to the latest, rather gradually work your way to the latest.

Make and model of the SSD as well?

 

[Fix_that_Glitch]

Take a close look at the second slot make sure nothing is bent, dirty or blocking the ram from seating properly.

 

[Fix_that_Glitch]

You can also try unplugging cord, removing battery then hold down the power button for 30 seconds. Then put battery back in and plug in to outlet and try a restart.

 

[DescL]

Thank you both for you answers.

@Lutfij
I have uploaded the pictures on Flickr. CPU-Z screenshots and photos of RAM-sticks and SSD.
Photo's specs RAM & SSD
On one photo you can see a ram-stick inserted in the working slot, other slot does not work.

@Fix_that_Glitch
I have looked at the slot, all pins seem perfectly fine.
I have tried your trick, strange thing happened. I rebooted and it worked perfectly, made it to home screen. Then suddenly screen went black again. Only getting ram-stick out of (defect?) slot made me able to boot again.