Here are some basic Windows commands that are good to know!
This one is cool:
System File Checker verifies the integrity of and repairs Windows OS dll files. For Windows XP it will require you to insert the original Windows XP install CD.
To repair file system errors, boot a Windows CD to recovery mode, then run
chkdsk /r /v
For Windows 7 at the recovery command prompt, you may have to issue:
chkdsk /r /v c:
This can take a very long time. Slash ‘v’ is verbose and will give details of the process in action.