so I haven't moved around any images or files or anything recently,
Apparently Lightroom disagrees with you. The reason you get the question marks is because you move files or folders outside of Lightroom, or rename them, or delete them.
The solution is here: Adobe Lightroom - Find moved or missing files and folders
I've followed those instructions, and instead of locating the photo, it opens a folder on my desktop which does not contain the image in question. I understand the reason for the question marks, but I'm confused because, regardless of what Lightroom "thinks", none of my images have been moved or renamed. In fact, they are in their original location on my hard drive. Any ideas as to what is going on and how I can fix it?
In the Library module, right-click on one of the "missing" images, "open in explorer" to see where Lightroom thinks the file is.
If this is the wrong location, using the folder tree on the left, correct the location of the folder containing the images.
I've followed those instructions, and instead of locating the photo, it opens a folder on my desktop which does not contain the image in question.
You have to point Lightroom to the proper folder that NOW contains your photos, which may not be the folder that initially opens (just like any other dialog box in any other program)
I understand the reason for the question marks, but I'm confused because, regardless of what Lightroom "thinks", none of my images have been moved or renamed.
Well, again, Lightroom disagrees with you and the way software works, it's very stubborn and the software doesn't care what you think. So until you can find the photos on your hard disk and reconnect via those instructions, you will continue to have this problem. So let's see if we can figure out why Lightroom thinks this is so.
What is your operating system?
What is the exact folder path, folder name and file name of one of these photos, according to you when you look at these photos in your operating system?
What is the exact folder path, folder name and file name of the exact same photo when you use the "open in Explorer" method explained by ManiacJoe?
Thanks. I selected the location of the folders/photos and all is restored. I wish I knew why this is happening. This is the second time something like this has happened. I'm using a Mac OSX 10.8.5 and I have Lr 4.4. Is it because I'm working with an older version of Lr? Has anyone else had this experience before?
This has nothing to do with your working with an older version of LR.
Have you renamed the external HD or top level folder (or any folder)? That could cause this to happen.
Has anyone else had this experience before?
Heh, it is a very common problem that appears here frequently. People don't understand what "importing" a photo into LR means (registering its name and location in the database) or they don't understand that not merely the immediate folder is listed, but rather the whole long hierarchy of folders from the drive name or letter to the photo file and that any alteration in that path will give LR indigestion. Sometimes the change can be caused without your being aware of it, by plugging an external drive into a different usb port than usual, for instance.
Thank you elie-d. Your explanation is clear and simple, easy to understand, and not only helps explain madena's problem specifically, but may also pertain to missing or unrecognizable files in general.