When I upload photos to my albums from my external hard disk, I don't get thumbnail images on my albums. When I upload from the hard disk of my PC there's no problem, the thumbnails have a picture. Why is that?

Sorry, this makes no real sense. An image is an image, no matter from where you upload it. Check if the images are not corrupt and look at your server's error log. Ask your host if you don't know where that is located.

Thanks, I'll look for it. It's really strange...