Try going to my computer, folder options, file types, locate the pptx, click advanced
create new action Open if needed or edit existing open.
Target to your powerpoint.exe location.
I've had to use a similar process for opening excel in safe mode when opening an excel attachment from email. In excel the standard app comes open with a /e. I don't have powerpoint installed on an xp station so I can't be sure of the exact command structure.
If the file is corrupted, then the only way to do pptx repair is to use online pptx repair tool PPTX Repair Kit. I mean, this is a local “online” and your data (if they are personal or secret) does not reach the server in the public domain. It is comfortable and protects your data from prying eyes. More I don't know how to help you. http://www.pptx.repair/