Back key & menu key isn't working

really need help for my samsung galaxy!! At first my screen used to get frozen so i used to do hard factory reset for it but still it used to persist often then once when i factory resetted my phone the touch screen started working perfectly fine!! but then the menu key & the back key stopped working! only the home key & other rest of the keys are working. i think its a software problem because the light still works when i switch on or whn i press the home button. I seriously need help!!

Thank you in advance!!!bold text