@Cathy516 I'm not sure what you mean- your whole calendar is greyed out, or just the dates this guest wants to book? And what do you mean "confirm" the guest. The host doesn't confirm the booking, it gets confirmed when Airbnb collects the payment from the guest. If it's just those dates that are greyed out, and say pending, that would mean that Airbnb is waiting for the guest's payment to go through and then it will be automatically confirmed.
If the whole calendar looks like that, if you are working in the app, try logging in on a computer, or switching to another browser. If still no good, contact Airbnb to solve it.