When I click on the Lr icon, I immediately get an "application error" message that says "The application was unable to start correctly. Click OK to close the application." What is going on?
Some help from you is necessary. Operating system Mac/ PC; what version of LR? was it working before?, is it the first time you are trying to use the program?
Did you encounter any problems with the install?
One thing you could check. Go to your Lightroom sub-folder. By default it is as shown in the screenshot. With Lightroom closed, if there is a file like the one hilighted like the one in the screenshot with a .lock extention delete this file. Then see if Lightroom will open.
When Lightroom is open it creates a temporary file with a .lock extention for the catalog file that is open at the time. If Lightroom is not closed normally this file can remain in place and will prevent Lightroom from opening.
If this is not the problem then we will have to try and see what the problem is, so let us know how you make out.
Try deleting the Preferences File