win10 not showing all installed ram

[1001101000z]

have a brand new asus f555 with i7cpu came with 8 gig installed(4gig built in and a 4 gig stick) win 10 64 bit replaced the 4 with an 8gig stick only showed 4 gig replaced the original 4gig stick back in only shows 4 gig stick is clean and seated correctly what can I do to fix thanks

 

[Tradesman1]

Could try resetting the BIOS to defaults then try reinserting the old stick - check for a BIOS update and to ensure it can take an 8GB sticks