Cannot open certain ppt files

[Menian]

Hey guys, really stuck here.
Right so I have a laptop running windows 8.1 and Office 13.
I have downloaded a series of Powerpoint files from my university website but only some actually work.
There are 2 in particular which are 97-2003 files. When I try to open them I get the message-box saying "Powerpoint can't open this type of file" - it then goes on to say it may be the wrong file type/corrupt etc.
Thing is I know there is nothing wrong with the file because my friend who has a macbook and office can open it no problem. Same file downloaded from same place/time etc. However, there are other 97-2003 files that open no problem too.

Really need some advice here folks as I have been unable to find anything online anywhere.

[JohnWilson]

I would first right click on the files > Properties and see if there is an UNBLOCK button.

It's also possible they are actually 95 or 97-2003 & 95 files (hard to tell). These will not open in 2007 onwards.
See PowerPoint cannot open the type of file represented by ....