It seems that .pps files somehow got associated with Windows Media Player. I would try to open PowerPoint and then go to File and Open and then browse to the file and try and open it that way. You will have to save the file from your email somewhere first. If that works then you can re-associate .pps files with PowerPoint. To do that you can right click the file and choose Open With. Then pick choose program even if PowerPoint is in the list. Then it will show you a list of available programs to open it with. If PowerPoint is in that list you can choose it and check the box that says Always use the selected program to open this kind of file. If its not there then you can click on browse and find the PowerPoint executable which should be C:\Program Files (x86)\Microsoft Office\Office16\POWERPNT.EXE for PowerPoint 2016 for example. Then it should open .pps files with PowerPoint from that point on.