Hello i have a windows 10 desktop HP 110-014 Desktop PC (ENERGY STAR)

Model #: H5P35AA

Model Name: 110-014
HD Bus Type: Serial ATA-300
Standard Memory: 4096 MB
Max Memory: 32768 MB
Number of Sockets: 2
Memory Comments: PC3-12800 1066Mhz DDR3 SDRAM DIMM 240-pin

I installed a second ram, of the same exact kind, but for some reason its only showing that i can use 3.5gb of it.
So it shows 8gb installed but only 3gb is in use, Any idea why?
Im using a windows 10 insider preview edition (latest build)