Well, this seems kind of obvious and a bit labor intensive, but have you uninstalled Word 2007 and AC, then rebooted and installed both again. If installing AC affected Word, I would install AC first.
I guess you could save to .doc rather than .docx and change .docx to .doc by renaming them before opening. Not sure if that would be a viable workaround or would work at all.
Good luck.
