Ray,
You may have already tried this but, go to the dog list; select the dog (collar) in question; click show information; click the 3 little bars on the bottom of the screen; select start tracking. Sometime in the past you may have stopped tracking that dog (collar) and forgot to select start tracking again. Therefore every time you turn the box or collar on, it will show you where the dog was last tracked with a question mark. Like I said, you may have already tried this, but myself and the guys I hunt with have done this ourselves on many occasions. The only other thing that I know of, shy of sending the collar back to Garmin, is to do a master reset of the collar. You will have to hold the button on the collar for about 20-30 seconds and it will reset the collar. I don't know if this helps you, but hopefully this will correct your collar problem.