Did you disconnect your chassis (engine) battery when you put your 24G into storage? Given the Sprinter's unique ability to completely discharge the engine battery in 2-3 weeks, you may simply not have enough voltage to run the Radio/Nav unit. Try flipping the radio power toggle switch to house batteries and see if that works.
If you still have problems, check your manual on how to reset the radio.
Roger & Mary
2017 Winnebago Navion 24V
2014 Tiffin Phaeton 36GH (Sold)