The sixth edition of the APA manual requires that you first cite the name of the author of the PowerPoint presentation, with the last name first, followed by a comma and the first initial, ending with a period. Put the date of the presentation in parentheses, followed by an outside period. The italicized title of the work should follow, with the words “PowerPoint slides” in brackets before the period. Write “Retrieved from,” without quotation marks, then provide the URL address for your source. For an in-text citation, "signal" the author's name at the beginning of the sentence, summarize the gist of the PowerPoint and then close the sentence with the date--and the date only--in parentheses.
You face two choices if you're citing a PowerPoint from a non-online source. The first choice is to follow the same format as if the slides came from an online source, but eliminating the words "Retrieved from" and a URL. The second choice is to treat the PowerPoint slides as "personal communication." In this case, write a signal phrase in the text by introducing the name of the author, followed by an explanatory sentence of the slides. The words "personal communication" and the date should follow in parentheses. It would look like this: "Don Hastings found that students don't read even assigned chapters unless they know they will be quizzed on the content (personal communication, April 1, 2013)." As personal communication, this information would appear only within the text of the paper; it would not appear on the references page.