PSVITA on/off button not working

Hello! The Psvita turns on and it lets me press the screen and iniciate some games, but when I try to return to the home menu, the PS button wont work at all, not responding. Furthermore, also when it turns on, wont let me turn it off by pressing the on/off button and sometimes, it will turn off automatically as if i was pressing the button (long press, because it goes absolutelly off). I have tried to replace the on/off flex with various of them, but still the same problem. Could it be the mother board? How could I know and solve it?