I have a samsung g600 but the top part of the buttons wont work what can i do?

Hello !

Your phone innner key pad is damaged thats why is not working the best solution ( test) I suggets a technician to swap the innner key pad to see if okey .
Beacuse sometimes stuff like steam ,juice ,water form a coating ( rust ) that affect the pad plates and brings poor contact , Also the mother board key pad contacts should be cleaned .

Good luck