Upgrade options?

It’s probably better to just save up for something brand new instead.

Hey there!
So, I just added another 8 GB of RAM to my rig—now I've got 2xKingston Technology HyperX Fury Memory Blue 8 GB 1866 MHz DDR3 in there—but my system (running Windows 10 home 64) is acting a bit weird. It shows that I have 16 GB installed, but it says only 7.97 GB is actually usable. If I check Task Manager, it says 8 GB is being "hardware reserved." What does that even mean? I'm kind of stumped as to why it won't let me use all the memory I paid for.
I tried digging around online for some fixes, maybe messing with those MSConfig settings, but nothing seems to work. My setup uses a Gigabyte GA-970A-DS3P motherboard, and I'm pretty sure the sticks are seated correctly—I originally had the first one in the second slot and put the second one in the fourth slot.

Maybe try moving them to the last two slots and just resetting your BIOS to defaults

At this point, I guess my only move left is to try swapping the slots around. My BIOS says everything looks totally fine—it’s reading all 16 GB of memory—and CPU-Z is showing the exact same thing. Since they're identical sticks, there shouldn't be any compatibility issues at all, so I'm honestly just scratching my head over why this is happening.

Hey,
I'm looking to upgrade my motherboard and CPU, so I could use some advice. Here's what I'm running right now:
ASUS M4N68T motherboard with AMD Athlon ii x4 640 processor
AMD Athlon ii x4 640 3.0 GHz
G.Skil Ripjaws series 4GB (2 sticks)
Kingston SSD 240 Gb and Hitachi 1000 GB sata
Gainward GeForce GTX 960
OCZ 550 w

I use this rig for both work and gaming. Ideally, I want to pick up a setup that I won't have to touch again for at least the next five years (specifically regarding the mobo, CPU, and RAM). I put together a potential build, but I wanted to check if there's a better way to go or if this is solid. I'd love to keep the total under $1833, though I might stretch it if the parts are truly top-notch.
https://ibb.co/mbbZdz

Corsair Vengeance 16GB (2x8) DDR4 3000MHz
ASRock B450M Pro4
Cooler Master Devastator 3 keyboard + gaming mouse, 7-color LED lighting, US layout

2 $100 - Micro Center

Intel Core i5-8400 box, s. LGA1151, 3.4GHz, 19MB cache, Hexa-core, Wraith Stealth
Cooler ARCTIC COOLING Freezer 33, socket 1151/1150/1155/1156/2011-v3/2011/AM4
650W Power Supply, ANTEC HCG650 Gold, ATX v2.4, 120mm fan, modular, 80+ Gold

$0.79 - Best Buy