My dad had lost his CD, and Microsoft didn't help provide me with a download (Office 2007 not supported anymore since October), so I had to download a torrent copy of it, and also the Office 2007 SP3 update file. I used Belarc Advisor to show his 25-character key (in the Software section of its report).
Uninstalled Office 2007 from Programs and Features, didn't tinker with removing remaining folders/files, and just re-installed with the download copy, entered the key, updated to SP3, and everything was recognized and working again no problem.