First step is to see if its your catalogue where the problem lies or with the app or plug-in. Try opening another catalogue, or if that does not work then create a new catalogue. Option-Click on the Adobe Lightroom icon and when it launches it will prompt you to open an existing catalogue or create a new one.
Yesterday I could create a new catalogue but once I had closed the catalogue it would not re-open.
Once you have ruled out the catalogue which is unlikely you can try resetting your preferences.
The following is direct from Adobe’s website:
Reset your preferences
To reset your preferences, do the following:
- Quit Lightroom.
- Navigate to the preferences file:
- Mac OS: /Users/[user name]/Library/Preferences/com.adobe.Lightroom5.plist
- Windows 7, 8: C:\Users\[user name]\AppData\Roaming\Adobe\Lightroom\Preferences\Lightroom 5 Preferences.agprefs
- Drag the preferences file to the Recycle Bin (Windows) or Trash (Mac OS).
Recent versions of Mac OS have hidden the Library folder under the user account so a quick way of getting there is to press Command-Shift-G then in the box type:
This will take you to your library folder where you can find and delete the preferences file.
This fixed many issues in Adobe Lightroom V4 and V5 but it did not fix mine.
The next step is to disable your plug-ins, you might wonder how if Adobe Lightroom is hanging on startup but if you remember to hold the Option key as you click on the application icon, create a new catalogue then once in disable your plug-ins.
If this fixes your issue you can then start up a plug-in at a time, shutting down Lightroom and restarting each time until you find the plug-in that causes the issue.
You can then replace the plug-in which should fix the issue.