It is important to clarify. Many people posting use the term "template" to mean a model document in the .docx format. In Word jargon, it means a .dotx or .dotm file. I assume you are using it in that sense.
Such templates are normally not opened, rather a new document is created based on the template.
Repairing / re-installing will not help with a corrupted document or template.
If you can open it in safe mode, can you copy everything except the last paragraph mark in the template and paste into a new template?
Otherwise, do you have an older backup from your computer that would have the template before it was corrupted?
If you obtained this template from an external source can you get a new copy?
I am curious, how is it that your content is stored separately from your formatted document?