Thanks Carl, but how would they all have become detached from the projects in just a few days? It's all my completed or in-progress projects so for most of them the files have been deleted. If I did find them, I'd have to re-do the project from scratch, wouldn't I?
No, you do not have to do the project from scratch.
Restore the missing files to the hard drive. Open the .PDS file that is the project file, when the window comes up to browse or cancel, choose browse, and navigate to where you stored the media file(s) on your hard drive.
PD will then load the file(s) into the project library and timeline.
The best way to store your projects is to Pack Project Materials from the File > Export menu.
That will copy all of the media files and the project file to the folder you specify. It will write all of the media that is in the timeline to the pack project folder. If you have other media in the libary, you can also copy that media to the Pack project folder.
Everything will be in one place.
Carl312: Windows 10 64-bit 8 GB RAM,AMD Phenom II X4 965 3.4 GHz,ATI Radeon HD 5770 1GB,240GB SSD,two 1TB HDs.