Hi Lynn -
Not much information to go by there, but the first thing I'd check is Project Settings > Metronome (or right-click on the Metronome icon up top) to make sure the click hasn't gotten turned off -- remember, there's an independent Click on/off setting for recording and playback. I suppose you even could check the Click object (Environment Click & Ports layer), but I'd think it's much more likely to be something simple, as above..
