See article How to reset security settings back to the defaults Using SubInACLhttp://www.winhelponline.com/blog/reset-the-registry-and-the-file-permissions-in-windows-xp/
Also reset the file associations for all files.. there is a fix around that can fix all file associations but I can't seem to remember the name or download site, but you can find a fix for individual filetype associations in the Doug Knox website, including the .exe file association fix. http://www.dougknox.com/xp/file_assoc.htm
you can also find other filetype association fixers for you other files in the drive.
Also this link may help: http://www.dougknox.com/xp/tips/xp_easy_file.htm