PVP 3 does not manage media automatically; this means that it is not actually copying media to a particular location on your machine. Instead it notes the file path of the media and creates a link to it in the application.
So if you had media on a removable hard drive, flash drive, or network drive which was removed from the machine or otherwise made inaccessible, PVP 3 will not be able to access or trigger the media in question, as when it attempts to access the media at the saved file path, it will not be able to resolve the file path.
If you need to move a show file and all associated content to a different computer then we recommend using the Relative Media Path feature; see this Knowlege Base article for more information.
One way to help ensure that your media is always available when needed is to make sure that it is stored on a local disk internally in your machine. This can be a system disk or secondary disk, but should be something that cannot be ejected or removed as this will help ensure that you can trigger your media.