Just bought a new computer and loaded Lightroom 5 onto it. It won't work and I don't know why. I've seen two error screens. Photoshop works just fine.
How did you install the application e.g. from disk or download?
You can't use a migration tool from an older Mac.
Try sending it to the trash and try the latest version 5.7.1 from this download link:
Retrieving data ...