Either blinks OFF in the top left end of the monitor (next to the battery symbol) or F-- in the top right. Wouldn't take picture in either condition, which seems to occur randomly (but way too often for comfort, had to get a small back up camera not to have a holiday ruined). Switching on/off, taking out and recharging the battery, resetting didn't help. Mine is not a body only, though, a set bought in 2005.

Cameras - Nikon - D - D50 Digital Camera