This whole issue is easier to live with than to troubleshoot. Reinstalling is a royal PITA and may not even be possible ...
A possible workaround that may
* coexist with your Office 2008 install is
Office 2016 for Mac Preview. It
iooks good and seems to work well, but check the
FAQ.
*) The preview is only listed as usable alongside Office for Mac 2011, but this compatibility may apply to older versions of Office as well.