Couple of things to try:
What happens if you copy the powerpoint file to your computer hard drive, then open powerpoint and try to open it directly? (i.e. not by double clicking it.
Are you sure the file extension is .ppt and not .pps? You might need to go to the Organise menu, file and folder options, view tab and untick the "Hide extensions for known file types"
Let us know how you get on.