Tried everything but it still won’t turn on

@evaneng since those were alkaline batteries the nickel on those contacts has been causticaly etched away. Use a long cotton applicator and mix some white vinegar and sterile water (about a 50/50 mix) and use the applicator to clean of more of the residue. It will not be shiney but will from now on continue to be rather dull looking. That is okay, for as long as you keep it from getting worse. After cleaning it with vinegar/water, use some high grade isopropyl alcohol to clean that off. Then apply some dielectric grease to those contracts. Nothing layered on just a fine coat will do.