Hi @adelsondamar
If you press harder, does it works?
one thing you can try is to open up and check on the buttons and microswitches.
check for any dry solder joints or worn out micro switches on it.
those micro switches sadly now has a limited lifespan..
You can use the multimeter in beep community (digital) or resistance (analog) to test the microswitch.
depress the switch and it should beep, or the analog pointer will move.
I would suggest you to replace the micro switch, which you can order it from ebay / aliexpress, etc.
To replace the micro switches, you need to have some soldering skills, perhaps I say it is not so difficult, else you can ask you friend for help.