How to delete windows.old in windows 7 or undeleteable files & folders

1ST METHOD

To delete the Windows.old folder from an earlier installation of Windows, follow these steps:

1. Click Start, type disk cleanup in the Start Search text box, and then click Disk Cleanup.
2. In the Disk Cleanup Options dialog box, click Files from all users on this computer.
3. In the User Account Control dialog box, click Continue.
4. Click to select the Previous Windows installation(s) check box, and then click OK.

Advanced users can also use a command prompt to delete files and folders from an earlier installation of Windows Vista. To do this, follow these steps:

1. Click Start, click All Programs, click Accessories, right-click Command Prompt, and then click Run as administrator.
2. In the User Account Control dialog box, click Continue.
3. At the command prompt, type takeown /F <DriveLetter>:\<FolderName>\* /R /A, and then press ENTER.
   
   Note When you run this command, you are granted ownership of the administrator group for the folder, of all the subdirectories in the folder, and of all the files in the folder.
4. At the command prompt, type cacls <DriveLetter>:\<FolderName>\*.* /T /grant administrators:F, and then press ENTER.
   
   Note When you run this command, administrators are granted full rights to all files and to all folders.
5. At the command prompt, type rmdir /S /Q <DriveLetter>:\<FolderName>\, and then press ENTER.
   
   Note When you run this command, all subfolders and all files in the specified folder are deleted. Additionally, the specified folder itself is deleted.

2nd METHOD

I know what you're going through.  I had two aborted attempts at installing Windows 7 and it left two huge .old files on my drive.  The answer the others are giving is if you are deleting them from a Vista OS.  You, like I was, are trying to delete them from the Windows 7 OS .  Here is how to do that:

Click on Start/All Programs/Accessories/System Tools/Disc Cleanup
When the dialog box comes up, select the drive that has the .old files on it and click OK
The system then scans for the files to be cleaned up and another dialog box opens with the selection.  Click on the button labeled Clean up system files at the bottom of that dialog box.

Another dialog box will come up, select the drive again that has the .old files on it.  The system will perform another scan for the system files that need to be cleaned up.

After scanning, another dialog box opens up and there you will find a list of check boxes.  Scroll through and check on the box labeled Older versions of Windows and clickOK .

That should take care of them.  The two aborted install attempts I had as .old files where taking up 16 gigs.  This got rid of them.

3rd METHOD

Click Start> All Programs> Accessories>>right-click "Command Prompt", and then click Run as administrator.

run following 3 commands on command prompt

takeown /F c:\Windows.old\* /R /A

cacls c:\Windows.old\*.* /T /grant administrators:F

rmdir /S /Q c:\Windows.old\