Does Dell Diagnostics give you the ability to run an extended HD scan in addition to the Quick Test? Run the Quick test again to confirm it and see.
If not then you can determine the HD maker by looking on the HD or googling the serial listed under storage in BIOS setup, then run the maker's HD Diagnostic
extended CD scan. If it's WD then use the Data Lifeguard bootable scan on Hiren’s BootCD 15.1
since WD is too incompetent to keep a working ISO to download from their site.
You can also run Partition Wizard Check File System
from Hirens or run the comparable Disk Check
from the System Recovery Options
Command Line. Running these tests will confirm beyond doubt the HD's condition and whether it is reparable.
Or you can just replace the HD by googling the make/model for a replacement. There is probably also a video showing how to replace it for yours or a similar model.