On a PC
At the bottom of the clock, the Online Backup icon should appear if the program is running. The icon looks like a small padlock. When the program is working, arrows appear instead. If the icon is not there, you need to check why the program is not running.
On a Mac
In Mac OS X, check the application icon in the system tray in the upper right corner of the screen (by the clock). The icon is a padlock. When the application is working, an arrow appears instead. If the icon is not present, you need to check why the application is not running.