2. Run Disk Check (CHKDSK) to Repair Disk Errors:
Open Command Prompt as Administrator: (As described above). 
Run CHKDSK: Type chkdsk /f /r /x G: and press Enter. Replace "G:" with the drive letter of your Downloads folder's location (e.g., "C:" if it's on your main drive). 
Note: The /f parameter fixes errors, /r locates bad sectors and recovers readable information, and /x forces the disk to dismount before checking.