I am new here, and a long time mac user with Tiger 10.4.10.

Imagine my end of year shock to find today that after a save to an external drive, when all is done and back in my usual Mac HD mode, that double-clicking on a folder, or file on the desktop does not open the folder nor "find" the app to use. I feel like the Tinperson in the Wizard of Oz-the heart of my system is gone! The good news is that when I go to finder I can open stuff manually and the stuff is all there.
Please tell me that this some incredibily simple thing that I have taken for granted all of my OZ like (I am into the happy metaphor, but inside I am freaking out) mac life! Thanks,

It sounds like your document aliases are messed up, or outdated. If the original files open fine, try making new ones. Click on the original, hold down the command (apple) key + L. This will create an alias. Throw the alias back on the desktop, or where-ever you'd like. If this doesn't work, I recommend downloading MainMenu. If there is truly is an issue with your file handlers, this program has tons of maintenance jobs, in one easy to use package.

http://www.santasw.com/

Have you tried repairing permissions with Disk Utility? If that doesn't work, can you try working at the terminal? Open it up (it's located in Applications/Utilities), and run the following commands:

$ cd Desktop
$ ls -al

If everything looks good in there, try typing cd "a_folder_name" , replacing a_folder_name with the name of a folder on your desktop. If that fails, then there's something wrong with your filesystem.