Tie at the bottom so the bird cannot move his wings. Put him in a box or wrap in a cloth so he cannot see. Watch that there are no ravellings to wrap around or choke the bird. Place the bird inside a paper bag and place in a very quiet place. If it hasn't recovered in one hour call a licensed wildlife rehabilitator or the WMC for phone numbers if you don't have them.
Birds see their reflections in windows and think intruders are in their territory.
Cover glass on outside of window with paper or smear with cleaning compound. Darken the room and leave a window or door open. Birds will be attracted by the light and fly out. Look for the nest. It should be very near.