i use a mac and my lightroom won't start up. any reason why? it just stays on the home screen like its loading.
Try restore the default preferences for Lightroom.
Press the shift + option keys immediately after you restart Lightroom, and select Reset Preferences from the resulting dialog box.
Let us know if that helps.
Which version of Lightroom are you using?
If using Lightroom cc,Go to your CC app, go to the top right, left click and check preferences and then sign out, and then sign back in. You may referSign in and sign out to activate Creative Cloud apps for the same.
Ensure your Lightroom version is up to date.See Keeping Lightroom Up-to-Date