I used Word (2011 Mac) to create a revision file a few months ago. The file contained numerous equations created with equation editor. I just opened the file for the first time in months and now word seems to have converted all the equations into images and won't let me edit them anymore.
It may be that, but it also may be that you don't have Microsoft Equation Editor installed. Check your Office installation, make sure you have all the components installed and enabled. This is usually the problem with "typical" installation which lets out many stuff. I always select custom and enable all components to make sure I don't face such problems. If you have the DVD-ROM of Microsoft Office, start the setup and add all the missing components.