Read about mixing computer memory.
Identify your motherboard with powershell. See if your choice of motherboard and cpu supports 16GB of the type of memory you have installed by reading your manual.
Get-WmiObject -Class Win32_BaseBoard | Format-Table Manufacturer, Product, SerialNumber, Version
Identify your memory with powershell:
Get-WmiObject win32_physicalmemory | Format-Table Manufacturer,Banklabel,Configuredclockspeed,Devicelocator,Capacity,Serialnumber -autosize
If you have used a supported amount / type of memory read the following.
Windows 10 Won’t Use Full RAM
- Windows 32-bit can only use up to 4GB of RAM.
- If you have an integrated GPU you cannot use the full memory as an integrated GPU uses memory from your RAM.
- Defective RAM.