Here, i searched it and found this:
Disk Defragmenter - C:\Documents and Settings\All Users\Start Menu\Programs\Accessories\System Tools\Defrag
Try that.
First, It's called "Disk defragmenter"
Secondly, it's a shortcut to "%SystemRoot%\system32\dfrg.msc"... and you cannot run shortcuts from the command line or Run dialog, AFAIK.
As such, the real recommendation should be to run
"%SystemRoot%\system32\dfrg.msc"
EDIT: if that file doesn't exist, and your chkdsk is missing as well, try looking in
system32\dllcache of your windows folder- chkdsk.exe and defrag.exe are both present here on my PC.
For that matter- try SFC /scannow on the command line as well. remember to include the space between the slash and the command, which is likely the reason your attempt to use chkdsk also failed (no spaces)