Just a small additionla note on CHKDSK C: /f
This command won't execute until the next reboot on the C: drive.
See output below...

C:\>chkdsk c: /f
The type of the file system is NTFS.
Cannot lock current drive.

Chkdsk cannot run because the volume is in use by another
process. Would you like to schedule this volume to be
checked the next time the system restarts? (Y/N)

Regards, Bill