This problem just started recently and I can not work out why.

I have no problem inserting a video clip into a power point presentation and it plays on my screen when I go the SlideShow ... but it does not work through the projector. I have tried several different projectors and none of them show the video clip being payed in powerpoint on my slideshow. This is something that only that started happening recently. I assume its some sort of settings change, but I can not find it! The projectors do show the video clip when I show it in WMP.

OS is vista

Any help or hints would be much appraciated.