Hi! Thank you for your response. I had previously encrypted the files while I was using MS Office 2003. I was attempting to resolve a problem with PC Tools Spyware Doctor & Norton Internet Security 2006, and on the advice I received from NIS I deleted some files which resulted in Windows XP professional crashing. Since I had made backups of my important files, I re-installed Windows XP after formatting Drive C. After installing Windows XP and other programmes, I also installed MS Office 2007. All files previously encrypted with MSO2003 refused to open. I then uninstalled MS Office 2007 and installed MS Office 2003 but the files still refused to open. I suspect that with the re-installation of Windows XP, I may have deleted some files that had been stored in C:\windows or C:\program files that had vital encryption information. I tried using some conversion software, but that too failed. I wonder if you can provide a solution, otherwise it will mean lot or work for me. Hi!!