In the Library grid, are you are getting the images marked as missing "!" ?
Right-click one of them, select "show in folders panel". Is the folder marked as missing? "?"
Right-click on the image, select "show in Finder". Is the picture on the hard drive at that location?
In the library it shows in the historgram that the file is missing. All the folders I have developed over the years have Q marks next to them. I have tried everything to relocate the files with no luck. When i chose “show in finder” nothing happens.
Assuming all your images were on an internal hard drive and not a disconnected external drive, using Finder, can you manually navigate to where the images should be? Are the folders and files still there?