Locate a shortcut to a text file on your desktop.
Right click on the shortcut and select Open With.
Select Notepad as the application. Do not pay any attention to the check box that says “Always use this type of file” that is checked off by default. This is important. Do not touch the checkbox.
Observe that all of your application files now have .lnk tacked onto the end of the name and no matter what application you try to run it just pops up Notepad and displays the binary content of the lnk file. What a mess! You can’t run anything.
If you actually did this. Then you really need to clean this up. This is going to take some research. Find out where the file associations are stored in the registry. Find the entry for .lnk files. Remove the notepad association.