|The reason for running chkdsk is because even a transient drive issue will prevent full defrag.|
You could start with chkdsk /f as this is quite fast and might do the trick. It fixes errors. Otherwise do chkdsk /r but this is more thorough and mike take an hour or so.
For what these commands do type chkdsk /? and it will tell you.
Note the single space before the /f or /r or /?
You will have to reboot after you input the /f or /r commands and it carries out the check before Windows restarts.
Always pop back and let us know the outcome - thanks