If anyone has ever encountered this issue I had to deal with, here is how I fixed it:
First of all, I went to my motherboard manufacturers website and downloaded latest CAP file (I have Asus motherboard) that allows me to update my BIOS. I put the CAP file in an USB flashdrive.
I went into BIOS, and took EZ Flash update (I don't know how about other BIOS', you may wanna look up some vids on YouTube on how to update your BIOS) and it updated my BIOS.
Next, I turned on the PC, however, the problem was still there: 4.1 GB hardware reserved ram, so I decided wait 1 day and next day after updating BIOS, I opened up my PC case and swapped the RAM sticks (I just replaced the positions of the RAM), however, that didn't work, so I put the RAM sticks back in their original slots. I started up PC, and, well, the 4.1 GB reserved is still there.
HOWEVER, THE NEXT DAY I turned my PC on, the RAM issue was gone. Like, I don't know what happened but it's gone. Hardware reserved is currently sitting at 56.5 MB. And it actually shows 7.9 GB, not 3.9 GB as MAXIMUM.
Whoever is having this issue: Update your bios, maybe take out your RAM sticks and remount them in the sockets, and then give it time, maybe it will help.
P.S I know this is a thread ''necro'', but I finally fixed this issue that has been pestering me for a year.
good luck