RETRY BECAUSE THERE IS SOME DROSTE EFFECT HAPPENING:
It looks like you have the most recent version.
the media items such as Landscape01.jpg, Landscape02.jpg, Food.jpg and some .mp3 will appear automatically in your media room, when you open PD and/or start a new project AND in the preference setting (project) you have ticked the box "Automatically load sample clips when PD opens". Whe you untick that box, these media files will not show in the media room anymore.
The sample clips are especially usefull, in case you want to try something out, or if you want to share some trick or error that even is possible or occurs on the CL given sample clips.
The previously downloaded files are ususally stored in the folder: c:\users\public\Cyberlink\ You will find a number of folders that start with Downloaded. If they are not there then PD (obviously) cannot find your downloads. maybe you have a backup of these folders that can be restored (I am not sure whether PD also maintains some index to the downloads, in that case a simple restore will not help). If these folders ARE still in place and PD cannot find them, then I would not know what has happened. It would recommend uninstalling and reinstalling PD (after you have made a backup of the folders of course). Also check whether you AND PD have access to these folders(check the windows (security) settings for these folder. (It that case it may help open PD with administrator rights).
I would in case the folder are available and not recognised by the (updated) PD, also inform CL about this situation by filling for a customer query.