using all 4 ram slots - I have 16GB RAM but it's only showing 8GB. butterfly 888 slot

So I have 16GB RAM. After upgrading to Windows 10 however it says I only have 8GB. When I look in task manager it seems to know I have 16GB but for some reason only using 8Gb of it and for slots used it says 2 of 4 when I'm using all 4 RAM slots. I'm not techy at all but if somebody could explain to me why this is it would be appreciated. If it is something like just a broken RAM stick then that's easy to fix but I don't want to go out and buy a bunch of new RAM if it's a different issue.

If you have four RAM sticks and a four-slot motherboard, then you can just populate all four slots with all four RAM sticks.

– Using an r5 3600, I was unable boot with RAM in slots A2 and B2…had to use A1 and A2. ... RAM can work on 3533) -Hynix CJR. Cons: -Nope. 8. Jake S ...

To start with, test each single RAM stick in all of the 4 slots one by one and repeat the same for all other 3 sticks to check if RAMs / Slots are working or not.