Vista Tutorial - Problem opening pictures...

I am praying to the computer gods that someone on here has a solution to my problem. I use Windows Vista Home Premium edition.
I was running out of space on my Dell XPS 1710 Laptop and transferred all my photos and videos to an external hard drive. I plugged the hard drive back into my laptop and now I can't view any of my photos or videos. They are still there, taking up many, many GB's. And on a few of the pictures, I can see them on the thumbnail. However, when I go to open them a message pops up on Windows Photo Gallery saying, "Photo Gallery can't open this photo or video because it might have been deleted or is in a location that is not available."

I know I messed up bigtime by not backing them up. Is there any way to save my files or am I out of luck. Any follow up questions you got, send them my way. Appreciate the help. Thanks.

An addendum,

I have been opening the files straight from my external hard drive. When I attempt to copy the files to my laptop it says "Item not found...this file is no longer in the F: etc..."
When I unplug the hard drive and plug it back in, I can view about 50-60% of the pictures in thumbnails and even open them...but after a couple of minutes it gives me the same message about the file maybe being deleted.

Just a thought maybe worth a try, you say that the disk shows "many gbs" being used, have you tried plugging in the external hard drive on a friends computer ( xp or vista) , to see if you can open your photos? It may be a bad driver for your external hard drive that is fouling you up. If it does work else where then we will have some place to work from.