Question My memory upgrade won't work

[SkyWar 007]

So basically guys I removed the ram that came with the laptop to see what is it and put it in the same slot. Surprisingly the laptop didn't boot even tho I'm sure i didn't do anything wrong. The start button light for a second then I hear the fans and the hard disk sound and nothing. So i changed it to the second slot and it worked just fine.
And I got another 4 gb ram and its brand new i did put it the first slot same thing happened as before when I removed the original 8 gb from my laptop it worked fine with 4gb in the first slot
Can anyone know why this is happening

 

[sizzling]

Mixing RAM not bought as a kit is gamble. The 2 sticks may not work with each other.

 

[SkyWar 007]

Mixing RAM not bought as a kit is gamble. The 2 sticks may not work with each other.

But each one is working in a specific slot why is that

 

[sizzling]

But each one is working in a specific slot why is that

I thought the 2nd one worked in both?

 

[SkyWar 007]

I thought the 2nd one worked in both?

No the 8gb is working in the second slot and the 4 in the first

 

[Calvin7]

Memory is guaranteed in the form sold. Other combinations you decide to make have no guarantee to be compatible together.

If you have a question about memory, I suggest listing it by part number or link to it.