Lately, I started noticing that the new NVIDIA driver won't be installed, I tried deleting it and restoring it a few times, and one time when I did that somehow the audio driver got damaged (I have no idea how) - I started hearing differently from the usual.
While installing the NVIDIA driver correctly and trying to reinstall the audio driver, I thought it would be a good idea to check disk C, so I checked for a command to scan and repair the disk. I found the command chkdsk /f and ran it. The PC asked for a reset and I did. I waited and saw the repair go up to Stage 2 75%, 59% of the total process. Then I didn't notice exactly what happened but I saw that I needed to select a bootable device and restart the PC.
So I restarted the PC and went to BIOS to check for my C drive with the OS, when I noticed it was gone and only disk D was available.
What happened here and why can't I see disk C even thought I "did everything by the book"?