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I want to access files in one computer which installed windows XP, I don't have windows logon ID.

I press F8 and find I can't go to command line, if I go to safe mode with command, I still need to logon in windows.

is there any way I can make my thumbdrive bootable by MS-DOS and then access files or other way to go to MS-DOS during bootup?

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the passw for admin can be override, you'll just have to google up a tool.
You'll find such a tool on ultimate-bootcd for example.

There is also something for windows called CMDCONS which is a pre-OS boot tool used to repair various issues.

You can also use WindowsPE, a Windows operating system watered down to just Command Prompt and that can fit on a >1GB flash drive. All you do is boot off of the drive and run the commands you need.