Only half my RAM is usable, when I got my PC I didnt have this problem?

Hi, first of all, I got my PC in 2018 december, and right near the start I ran a test with userbenchmark and these were the results
Update: UserBenchmarks: Game 70%, Desk 80%, Work 75%
CPU: AMD Ryzen 5 2600 - 80.4%
GPU: AMD RX 580 - 72.4%
SSD: Adata SU800NS38 128GB - 84.1%
HDD: Seagate Barracuda 2TB (2016) - 94.2%
RAM: G.SKILL Ripjaws V DDR4 3200 C16 2x8GB - 79.7%
MBD: Asus ROG STRIX B350-F GAMING
Update 2: Only now did I do another test and difference seems to be half my RAM UserBenchmarks: Game 71%, Desk 76%, Work 64% CPU: AMD Ryzen 5 2600 - 77.9% GPU: AMD RX 580 - 73.7% SSD: Adata SU800NS38 128GB - 89.2% HDD: Seagate Barracuda 2TB (2016) - 97.4% RAM: G.SKILL Ripjaws V DDR4 3200 C16 2x8GB - 41.7% MBD: Asus ROG STRIX... show more Only now did I do another test and difference seems to be half my RAM
UserBenchmarks: Game 71%, Desk 76%, Work 64%
CPU: AMD Ryzen 5 2600 - 77.9%
GPU: AMD RX 580 - 73.7%
SSD: Adata SU800NS38 128GB - 89.2%
HDD: Seagate Barracuda 2TB (2016) - 97.4%
RAM: G.SKILL Ripjaws V DDR4 3200 C16 2x8GB - 41.7%
MBD: Asus ROG STRIX B350-F GAMING
Update 3: As you can see my RAM is "performing way below expectations" and when I check my system it says RAM 16GB (7.95 usable). The results are similar in task manager - Memory 16GB (usage 7.9GB) In use 3.8GB Compressed 46mb Committed 6.8/9.8GB Cached 3.6GB Paged pool 467mb Non-paged pool 161mb Speed... show more As you can see my RAM is "performing way below expectations" and when I check my system it says RAM 16GB (7.95 usable). The results are similar in task manager - Memory 16GB (usage 7.9GB)
In use 3.8GB Compressed 46mb
Committed 6.8/9.8GB Cached 3.6GB
Paged pool 467mb Non-paged pool 161mb
Speed 1067mhz
Slots used 2/4
Form factor DIMM
Hardware reserved 8.1GB
Update 4: Yes I tried msconfig and unchecked the full memory box, it wasnt checked to begin with, restarted my PC and the results are the same. But when I do check the box it does say 16000mb memory, but that doesnt explain why only half is usable now when it was fully usable months ago. I also checked several forums where... show more Yes I tried msconfig and unchecked the full memory box, it wasnt checked to begin with, restarted my PC and the results are the same. But when I do check the box it does say 16000mb memory, but that doesnt explain why only half is usable now when it was fully usable months ago.
I also checked several forums where people had the "only half my RAM is usable" problem, but none of them had the problem where first it was fully usable and then only half.
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