Check for corrosion on pins and make sure that you have enough power, not with volt meter but test light. It is probably not cost effective to repair older unit
It may be a dead battery and to replace that probably costs more than a new unit. Based on all the problems owners note here with Lowrance, let me be the first to suggest you get a different maker's product!
I don't know where you might find whether suspended fish, but when you get there, if you want better images than being rendered on your Lowrance elite 5 DSL, then get a better unit
