Error messages and crashing

I am editing a powerpoint created by a colleague and whenever I try to change something such as a character or a scene, I got an error message and then when I went to save the file it says the file is corrupt and cannot open so I had to shut down and lost all the work.  When I started a new presentation and went to add a character, it would load and let me see one character but none of the others and then eventually would not display the character selection photos to choose from.  When I cancelled and tried again, the menu went to the side of the screen and all froze up - again had to shut down.  Help, I have a really important presentation to do and it appears I cannot use this software.