Windows NT (all versions), Windows 2000, Windows XP, Windows 2003 all may give such an error message if someone does an "odd thing".
Your story doesn't have the OS or enough detail for me to hazard a guess. Except one. The MBR is not being rewritten proper. I usually just boot a WINDOWS 98 diskette, type FDISK /MBR to fix that, but before you say that's not how, there is a Microsoft KB article about this so go look it up.
Best of luck,
Bob
I have used a software(ez-tec sanitizer) to erase my hard drive in order to do a clean installation. Unfortunately, I received a message that says: NTLDR is missing. I tried everything to bypass this message a have a clean installation but my efforts are still vain. Can you please help me with this.

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