PowerPoint could not open the file.

I just want to highlight 2 points:
.pot files can be opened only by PowerPoint 97 to Office PowerPoint 2003. Is your system contains only these version of office. double check that.

https://support.office.com/en-us/article/File-formats-that-are-supported-in-PowerPoint-2010-252c6fa0-a4bc-41be-ac82-b77c9773f9dc

 Also, why don't you use the technique used in the below url, to view your ppt :

http://p2p.wrox.com/asp-net-1-0-1-1-professional/58388-how-open-word-doc-using-asp-net.html