Please do NOT add images via the "attach files" box, as you are then forcing everyone to DOWNLOAD the file to view it outside their browser. Drag/drop the image files directly ONTO your reply box so other users can see them without needing to download unknown strange files. Thank you!
If you watch the splash screen as the program loads after a few seconds you should text on the left side about a 1/3rd of the way down telling you what's loading. This can give you a clue if it get's stuck when something's loading. Could be a problem with a 3rd party plug-in. You can also reset your preferences to the default settings by holding alt when splash screen appears.
Try also to delete the media cache manually
go to Mac:/Users//Library/Application Support/Adobe/Common