No applications are working. How do I fix...

Go to start button > programs > accessories > system tools > system restore. Pick a restore point before you made the changes you did. If you have Vista and need to go further back, click on the button below that says pick a restore point older than 5 days. Let Windows reboot and your system will be restored back to that time.

It sounds like the files were deleted off the hard drive or moved to another location. Normally, when you have icons on the desktop they are known as "Shortcuts". What this means is the icon is directing the computer to the real location of the file.

So for example lets say you install a program like "Winamp" (A Music Player). When the program installs it actually puts the files for the program in a folder such as "C:\Program Files\Winamp\Winamp.exe" . Then it puts an icon on the desktop that points to that location. So when you end up with a question mark next to the icon it usually means the icon is pointing to an incorrect location and the file it is looking for does not exist there.

Like I said before a) it was deleted b) it was moved.

I am going to assume it was deleted as I don't see you randomly moving files around. You basically are left with no option, but to reinstall the software that is not working. If you do not have the original disc's or downloads, you could try a "System Restore", but that may not work. Below are instructions to do a System Restore in Windows XP & Windows Vista (not sure which you are running).

System Restore For Windows XP

System Restore For Windows Vista

As I said, if none of this works you basically need to reinstall the software.