I want to access files from my hard drive

My files are gone from the Desktop and Videos folders. The Documents, Downloads, Pictures, and Music folders, when tried to open, trigger a prompt that reads "Location is not available" among more text. Please, can someone help me get access to my files?

My laptop came with a 1 TB HDD. I bought and installed a new 1 TB NVME SSD. My plan was to fresh install Windows 10 on the new drive so that I could boot from it. Note that I want to keep the HDD so that I can still use it as extra storage. While downloading the Windows 10 installation media onto an USB flash drive my computer crashed and rebooted back into the HDD, but into a temporary account. After some research, I figured out a way to boot back into my original account so I could finish downloading the installation media and finally install Windows 10 on the new SSD.

Whenever I try opening the user's folder a prompt would read "You don't currently have permission to access this folder." The user's folder was not the only folder with this problem. Under the security tab, the owner of the HDD was not what I expected. I don't remember the numbers exactly, but it was something along the lines of "S- 1- 5- 21 - ...". While booted into the HDD I changed the owner from "S- 1- 5- 21 - ..." to myself. After changing the owner, the HDD recycle bin then got corrupted. (-_-) I tried clicking "Enable inheritance" (HDD Properties > Security > Advanced) and was able to open my user's folder.

Throughout the entire process I suspect I messed something up and caused myself to be in this position. I can't really offer you anything but help me out please. I'll try my best to make any clarifications if need be.

Additional Information:

HDD - TOSHIBA MQ04ABF

SSD - SHGP31-1000GM (SK hynix Gold P31)

HDD still shows that 36.4 GB are free of 914 GB. I think my files aren't gone but still somewhere.

Laptop was bought December 2018, so I suspect the HDD is not in great condition. Maybe I'm wrong and its performance mainly correlates with how full it is (878 GB / 914 GB).