Microsoft has some recommended methods for recovering from PowerPoint presentation corruption here, http://office.microsoft.com/en-us/powerpoint-help/recover-a-corrupt-powerpoint-file-HA001116878.aspx. S2 Recovery Tools for Microsoft PowerPoint provides easy access to most of these, allowing them to be engaged with pushes of buttons.
The program also adds four of its own independent methods. These independent methods include two text, slide and format recovering methods for PPTX files which repair all the salvageable underlying XML subfiles as well as the higher level conventional zip structure of these presentations.
The program also has links to three major commercial solutions. One of these is a web service provided by Recoveronix', Online File Repair. With the provided coupon code, until Nov. 1, 2013, the service is free, a $39 value.
I released this yesterday. It's one in a series of now 3 that includes S2 Recovery Tools for Microsoft Word and S2 Recovery Tools for Microsoft Excel.