Fixes for sync issues can range from easy to complex, but any solution will require you to take some action.Fix: If you do not see the tray icon, you do not have Dropbox installed on your computer.An update or change in either Dropbox or your firewall may cause the problem to occur even if it hasn't before, so check your firewall's settings.
Problems with individual files, like files incompatible with one computer's operating system, may cause files to sync correctly to all but that computer.
The Dropbox desktop app tracks these inconsistencies and will try its best to resolve the problem gracefully.
When it can't, the file will still sync to dropbox.com, but it may not appear or work properly on incompatible operating systems.
But the syncing on the i Phone (haven't tested it on my i Pad or Windows box yet) is a concern.
To make sure that your files are syncing correctly, first verify that your computers are connected to the Internet and are linked to the same Dropbox account.