Check the obvious stuff first. I know that some of those fishfinders are all self contained, if not check to see if there is an inline fuse on the power cord which might be blown, check any connectors for corrosion, make sure your battery(s) are fresh or fully charged, most finders won't work when the battery voltage falls below a certain level. Also, if you are hooking this unit up to an external battery, make sure the polarity is correct, that is the red wire goes to (+)positive and the black wire goes to (-)negative. If the wires aren't color coded try switching them on the battery terminals to see if that helps. Otherwise, like Mike said, if it isn't under warranty, ashcan it, bite the bullet and go for a new unit. Even if it is under warranty, you normally have to pay the shipping, and summer might be over when and if you get it back. Good Luck.