Difficult to say, but if you're absolutely sure the pump itself has water at the intake for it's use, and you're not some how just running the water in a loop,then it might be the pump. I personally wouldn't give up until I verified the valves all in...
Wild guess. From experience. Are you filling your water heater? It's the lowest point for water to run out. Especially if you have the plug/zinc pulled.
Usually there is some luan paneling covering that area from your 'basement or garage'. I've removed my paneling for quick access and a little extra special storage. Remember, these things are assembled by methods of simplicity. Someone put it togeth...
I suggest checking your batteries. See if they're swollen, hot, or actually have life in them. Sounds to me you've got one possibly soft causing issues. Or both for that matter. Plugged in you are still running off battery for those devices. Granted...